At least we have three days to catch our collective breaths.

After the first weekend of the 2018 NCAA Division I men's basketball tournament, the term March Madness has never been more appropriate.

Only two No. 1 seeds are left.

Only two No. 2 seeds are left.

Heck, the top four seeds in the South Regional are already watching from home.

It was a wild way to kick off this year's tournament, and we're just getting started.

So with the Sweet 16 matchups now set, let's take a closer look at the biggest X-factors in each of those games by highlighting a key player to watch from each team and the decisive battle that could determine the winner.

South Regional: (5) Kentucky vs. (9) Kansas State

Kentucky player: Shai Gilgeous-Alexander

SEC Freshman of the Year and projected lottery pick Kevin Knox is the headliner of Kentucky's all-freshman starting lineup, but it's Shai Gilgeous-Alexander who has been leading the charge of late.

Over three games in the SEC tournament and the first two in the NCAAs, the guard is averaging 21.8 points, 5.8 rebounds, 6.6 assists and 2.4 steals per game.

The 6'6", 180-pounder too could climb into the draft lottery, and he's the type of player who can almost single-handedly win a game when he gets going.

Kansas State player: Dean Wade

The Wildcats' leading scorer during the regular season at 16.5 points per game, Dean Wade has not played since the team's March 8 win over TCU in the Big 12 tournament while nursing a foot injury.

It sounds like he's going to give it go on Thursday in Atlanta.

"I am like 98 percent sure I will play. I don't know if they can keep me out of this one. This is big-time," Wade told reporters. "I'm excited. It gives me another couple of days to heal. I am starting to feel a lot better. My day-by-day gets a lot better. This gives me a few more days to heal and recover."

Facing a Kentucky team with so many dangerous weapons, getting the 6'8" forward back on the floor and contributing is a must if K-State hopes to keep this tourney run going.

Decisive battle: Half-court game

Kentucky has seemingly bought into the idea of being a defensive-minded team in the second half of the season, which will be put to the test against a K-State team that will try to slow the tempo of this one to a crawl.

If its freshmen can avoid lapses in the half court, UK is the more athletic team. If not, it could be a long day.

South Regional: (7) Nevada vs. (11) Loyola of Chicago

Nevada player: Kendall Stephens

When nothing else is going right offensively, the Wolf Pack can count on Kendall Stephens as a knockdown three-point shooter.

The senior has drilled a Mountain West Conference-record 126 threes this season at a dizzying 44.4 percent clip, and he's 8-of-18 in the NCAA tournament.

Digging a bit deeper, Nevada is 15-1 in games when he scores at least 16 points this season, compared to 14-6 when he's held under 16.

Loyola of Chicago player: Cameron Krutwig

The Ramblers are lacking in size aside from 6'9" freshman Cameron Krutwig.

While he's not the go-to guy offensively, he'll need to control the defensive boards and limit second-chance opportunities for the run-and-gun Wolf Pack.

Even if he's not counted on to shoulder the scoring load, he did put up 10.4 points per game, so he's capable of serving as a secondary scorer to Donte Ingram and Clayton Custer.

Decisive battle: Loyola's defense vs. Nevada's offense

Loyola is going to try to slow the tempo with its pack-line defense that has been a recipe for success. It's won six games in a row without scoring 70 points in any of those games.

Meanwhile, Nevada hung 87 on Texas in the first round and has averaged 83 points per game this season, which ranks 16th in the nation.

Something has to give.

West Regional: (4) Gonzaga vs. (9) Florida State

Gonzaga player: Zach Norvell Jr.

Gonzaga has no shortage of scoring options with five players averaging in double figures. That includes the duo of senior Johnathan Williams and junior Josh Perkins, who both played a significant role on last year's runner-up squad.

That said, redshirt freshman Zach Norvell Jr. is an easy choice as the team's X-factor.

The 4-star recruit has tallied double-digit points in six straight games, his longest stretch of the season, and he poured in a career-high 28 against Ohio State on Saturday.

If he has the three ball going again after hitting 6-of-11 from deep against the Buckeyes, the Seminoles will be in trouble.

Florida State player: Terance Mann

Terance Mann scored a career-high 30 points against Georgia Tech on Jan. 24, pushing his averages to 16.1 points and 6.2 rebounds per game.

In the 13 games since, he's scored in double figures just six times and his scoring average has plummeted to 7.8 points per game during that span.

The junior guard suffered a groin injury in the Seminoles' first-round game and was questionable against Xavier on Sunday before logging 10 points in 24 minutes off the bench.

He's capable of far more than he's shown over the past two months.

Decisive battle: Offensive efficiency

These two teams have deep benches and rosters that are stocked with athletic wing players.

It will come down to which offense at Staples Center in Los Angeles can build some momentum and limit turnovers.

The Bulldogs rank 12th in KenPom.com's adjusted offensive efficiency rankings and the Seminoles check in at No. 32, so scoring has been a strength for both teams all season.

West Regional: (3) Michigan vs. (7) Texas A&M

Michigan player: Charles Matthews

The No. 60 player in the 2015 recruiting class, Charles Matthews played just 10.3 minutes per game as a freshman at the University of Kentucky.

After sitting out last season following his transfer, the 6'6" guard has tallied 12.8 points, 5.5 rebounds and 2.5 assists per game for Michigan this season.

Matthews has scored 20 or more points seven different times this season, and he had 20 points and 11 rebounds against Montana in the first round.

Mo Wagner remains the focal point of the Wolverines attack and Muhammad-Ali Abdur-Rahkman is a consistent secondary option, but this is a different team when Matthews is playing up to his ceiling.

Texas A&M player: Robert Williams

Robert Williams is averaging 10.3 points and 9.3 rebounds per game while shooting 62.7 percent from the field.

The 6'10", 241-pound sophomore looks like a potential first-round pick in this year's NBA draft and creates a matchup problem for the perimeter-oriented Michigan roster.

He's averaging 10.5 points and 12.5 rebounds per game in the Aggies' first two NCAA tournament games.

Decisive battle: Michigan's post defense

Along with the 6'9" Williams, the Aggies also get significant minutes from the trio of Tyler Davis (6'10", 266 lbs), Tonny Trocha-Morelos (6'10") and DJ Hogg (6'9") in the rotation.

That's a lot for the 6'11", 245-pound Wagner to handle defensively, and the Wolverines will likely ask for significant action out of 7'1" sophomore Jon Teske, who has played just 12.8 minutes per game this season.

East Regional: (1) Villanova vs. (5) West Virginia

Villanova player: Donte DiVincenzo

With Wooden Award candidate Jalen Brunson (19.1 PPG, 4.7 APG) and potential lottery pick Mikal Bridges (18.0 PPG, 5.4 RPG) dominating the headlines, the consistent production of Donte DiVincenzo can sometimes go overlooked.

However, the sophomore guard has been just as important to the Wildcats' success this season.

He's third on the team in scoring (13.1 PPG) and he's made 75 three-pointers at a 39.1 percent clip, serving as one of the nation's most dangerous sixth men.

He also has the hot hand, coming off an 18-point game in which he knocked down five of 11 from beyond the arc against Alabama.

West Virginia player: Sagaba Konate

Villanova has one of the most dynamic offenses in college basketball, but Sagaba Konate has the rim-protection skills to force them into a perimeter-reliant attack.

The 6'8" big man has tallied 113 blocks on the season—second in the nation.

He also averages 10.8 points and 7.5 rebounds per game while protecting the back end with relentless defensive pressure, so he can truly be a handful on both ends of the floor.

Decisive battle: Offensive efficiency vs. defensive intensity

This matchup at TD Garden in Boston will see arguably the most efficient offense in the nation in Villanova go toe-to-toe with a West Virginia team built around its full-court press.

Whoever wins that battle wins the game Friday—it's as simple as that.

East Regional: (2) Purdue vs. (3) Texas Tech

Purdue player: Isaac Haas

All 7'2" and 290 pounds of Isaac Haas came tumbling down on his right elbow as he tried to secure a rebound against Cal State Fullerton in the first round Friday.

The result: A fractured elbow.

Haas tried to play in the team's second-round game, but the bulky brace he had wrapped around the broken elbow was not cleared by the NCAA and he wound up watching from the sidelines Sunday.

The Boilermakers have a lot of weapons, but getting Haas back will be key as he averages 14.7 points on 61.7 percent shooting, while also tallying 5.7 rebounds and 1.3 blocks per contest.

Texas Tech player: Zhaire Smith

Zhaire Smith has already made a name for himself during this year's NCAA tournament with his aerial game.

He can do a lot more than just dunk, though.

The 6'5" freshman has averaged 11.3 points per game this season and has provided a real spark since moving into the starting lineup at midseason.

He's played 37 minutes in each of the team's first two tournament games and scored 18 points on 8-of-13 shooting Saturday.

Keenan Evans is the Red Raiders' star, but Smith is capable of being a significant second weapon.

Decisive battle: Interior defense

The health of Haas plays a big part on the Purdue side.

If he can't go, it will be up to freshman Matt Haarms once again to control the paint against a Tech team that likes to attack the basket. The 7'3" backup played a career-high 29 minutes Sunday, tallying seven points, six rebounds and two blocks.

On the other side, Texas Tech is a fairly undersized team, so a healthy Haas setting screens for slasher Vince Edwards and leading scorer Carsen Edwards could create all kinds of matchup problems.

Midwest Regional: (1) Kansas vs. (5) Clemson

Kansas player: Udoka Azubuike

After playing just three minutes in the Jayhawks' first-round win against Penn, center Udoka Azubuike was a bigger factor against Seton Hall on Saturday.

The 7'0", 280-pounder had 10 points, seven rebounds and two blocks in 22 minutes.

That's still off his season average of 13.2 points, though, as he led the nation in field-goal percentage (77.5).

If he can avoid any lingering effects from the knee injury that has slowed him down the stretch, he adds another wrinkle against a stellar Clemson defense.

Clemson player: Gabe DeVoe

A reserve in his first three years, Gabe DeVoe has emerged as a key player for the Tigers, especially of late.

His scoring average jumped from 7.1 points per game as a junior to 13.7 points per game this year, and he's had six 20-point games since the beginning of Februrary—including 22 in each of the team's first two NCAA tournament games.

If he can continue to be a reliable second option alongside leading scorer Marcquise Reed, the Tigers will be that much more dangerous on the offensive end.

Decisive battle: Kansas' offense vs. Clemson's defense

Kansas has a bevy of offensive weapons with Wooden Award finalist Devonte' Graham, sophomore standout Malik Newman, sharpshooter Svi Mykhailiuk and the aforementioned Azubuike, helping it to the No. 5 spot in KenPom's offensive efficiency ratings.

Clemson has a defense that is ranked No. 7 in his defensive efficiency ratings and fresh off a stifling performance against a good Auburn team.

This Friday game in Omaha, Nebraska, might be the single best strength versus strength matchup of the Sweet 16.

Midwest Regional: (2) Duke vs. (11) Syracuse

Duke player: Trevon Duval

Trevon Duval came to Duke as a 5-star recruit and the No. 6 player in the 2017 recruiting class, so he's not exactly an under-the-radar choice as the Blue Devils' biggest X-factor.

However, it's been an up-and-down season for the IMG Academy product.

Case in point: He was held scoreless on 0-of-6 shooting in 30 minutes against North Carolina in the ACC tournament. Then he turned around and scored 19 points on 7-of-11 shooting and 3-of-6 from beyond the arc in the first-round matchup against Iona.

He's scored 15 or more points nine times and he's been held to six or fewer points 10 times.

It's boom-or-bust.

Syracuse player: Oshae Brissett

After a brief lull at the start of conference play, freshman Oshae Brissett has developed into a reliable second scoring option for Syracuse behind Tyus Battle (19.3 points per game).

The freshman is averaging 14.9 points per game on the season and went off for a team-high 23 in a four-point win over Arizona State in their First Four game.

He also tallied his 13th double-double of the season in that game, so he can make a legitimate impact on both ends of the floor.

Decisive battle: Syracuse's three-point shooting

Syracuse can catch teams off guard with its 2-3 zone sometimes, but Duke will be ready, having already seen the Orange in a 60-44 home victory.

That doesn't necessarily mean the Blue Devils will thrive against one of the nation's best defensive schemes, but relying on that to secure a victory will be asking too much on Syracuse's end.

Instead, they have to get something going from beyond the arc after shooting just 4-of-22 from distance in the first two rounds.

Battle (73 threes, 31.6%), Frankin Howard (67 threes, 32.8%) and Brissett (55 threes, 33.7 percent) are all capable of hitting from deep.

All stats courtesy of Sports Reference, unless otherwise noted.