When the Chicago Bears traded multiple picks to move up one spot in the 2017 NFL draft and selected North Carolina quarterback Mitchell Trubisky second overall, the investment raised serious questions. 

A one-year starter in college, Trubisky completed 68.0 percent of his passes for 3,748 yards, 30 touchdowns and six interceptions in 2016, but he struggled against more complex defenses with multiple fronts and coverages. In the Sun Bowl against Stanford, he tossed two picks, each to safety Dallas Lloyd, and demonstrated a disconcerting lack of field awareness. Trubisky has physical tools for days, and his stature, toughness and mobility are the traits a team would want in any quarterback if it could draw him from scratch, but he in no way appeared ready for the mental rigors presented to an NFL quarterback.

When he entered his first preseason game against the Broncos last Thursday with the Bears down 10-0, expectations thus shouldn't have been high. But then he completed 18 of 25 passes for 166 yards, a touchdown and no interceptions, adding three scrambles for 38 yards. While he did his thing against Denver's reserve defenses and relied mostly on short, easy passes, Trubisky looked more composed and consistent than expected.

"I thought he had a pretty good command of the game, but it wasn't all perfect," head coach John Fox said after the game, per Larry Mayer of the team's official site. "Obviously, you can see why he was picked in the draft where he was. I think that was evident. But we still have a long way to go as a football team."

Trubisky's performance was especially important to a Bears coaching staff that had to be disturbed by the performance of veteran quarterback Mike Glennon, who the team signed to a three-year, $45 million contract in the offseason. The Bears can escape that contract after 2017 with minimal salary-cap penalties ($4.5 million in dead money in 2018), but Glennon's $14 million cap hit this season is non-negotiable.

Chicago would be on the hook for $18.5 million in dead money if it cut Glennon this season, according to OverTheCap.com, which means the team is stuck with him even if he's unable to transcend a preseason opener in which he completed two of eight passes for 20 yards and a pick-six by Broncos cornerback Chris Harris Jr. that came on a horrible overthrow into a cluster of coverage. Glennon threw late most of the time, created his own pressure, failed to adjust to advanced defenses and generally looked far out of his element. Backup Mark Sanchez completed one of four passes for four yards and was a non-factor.

It was therefore important for Trubisky to impress, and he did.

"I thought it was fun," he told reporters after the game. "It was kind of what I wanted to do; go out there, just be consistent, move the ball with the offense, show command in the huddle, the line of scrimmage. O-line did a great job taking care of me. Running backs and receivers did a good job catching it and running it. I thought it was good. Obviously wanted to come out with a win, but we did a lot of good things."

As impressive as Trubisky was, the real star of Chicago's preseason opener was second-year offensive coordinator Dowell Loggains. He assembled a perfect game plan for a quarterback of Trubisky's physical tools and lack of experience with the things that make NFL quarterbacks great—diagnosing coverages in the pre-snap phase, reading defenses post-snap, going to his second and third reads and throwing calmly and consistently from the pocket.

Loggains had a raw player who has the velocity to make just about any throw and the mobility and size to present problems as a pure runner. The plan was to give Trubisky a moving pocket with boot-action concepts and first-read open receivers with various crossing and comeback routes. The use of pre-snap motion often helped Trubisky identify whether he was facing man or zone coverage. Though the Broncos weren't throwing as much at Trubisky as NFL defenses will in the regular season, he also faced a few blitzes and held things together for the most part.

According to Pro Football Focus, he completed two of six passes under pressure, with two receiver drops. That's hardly earth-shattering success, but it's better than anything Chicago's other quarterbacks did.

This touchdown pass late in the first half to Victor Cruz (No. 80), Trubisky's first in the NFL, is a good example of how a simple route combination can open things up for a young quarterback. Trubisky is rolling to his left after the snap, while left outside receiver Josh Bellamy (No. 15) runs his route into the end zone, taking cornerbacks Brendan Langley (No. 27) and Chris Lewis-Harris (No. 39) with him. Lewis-Harris is covering Cruz from the slot, but he follows Bellamy instead of Cruz, who takes a simple outside route on an easy path to six points.

What you want to see from any quarterback is the ability to throw with timing and anticipation to a certain spot on the field where the receiver is supposed to be. Trubisky showed this with a 24-yard completion to Deonte Thompson (No. 14) early in the fourth quarter.

Thompson's motion from left to right pre-snap gives Trubisky an indicator, based on defensive movement, that the Broncos will be playing zone. He knows that if he hits Thompson on the deep vertical route with the correct timing, it should be a fairly easy completion. Watch how he hits Thompson before the receiver is fully backed up into the phalanx of Broncos defenders. Quarterbacks who throw late into such situations tend to get their receivers beaten up, but Trubisky nailed the timing and rhythm aspects of this play.

On this 13-yard pass to Tanner Gentry (No. 19) later in that same drive, Trubisky showed he has the guts to give up the easy completion when he sees something better downfield and the nascent ability to make those tougher completions happen with velocity and ball placement. Here, he has tight end Daniel Brown (No. 85) on an easy short completion after Brown motions from left to right, but he doesn't take it. Instead, he rolls right off a boot-action concept and waits for Gentry to run his over route from left to right, hitting him to the correct shoulder away from the defender. That's a big-league throw, no matter who you are.

That isn't to say Trubisky was entirely ready for prime time. At least two of his scrambles appeared to be based on closed receivers and an inability to extend the play for those targets to get back open, which corresponds with his college habits. It isn't a big deal in the short term as long as Loggains keeps designing easy openings in the preseason, but it'll matter a lot more as time goes by if he can't improve his diagnostic abilities.

And if Trubisky continues to outperform Glennon, the question will be more pressing as the preseason goes on: Why not start the rookie if the veteran proves that he just can't cut it? Glennon is a quarterback with fixed and considerable limitations. While he's been in the NFL since 2013 and has started 18 regular-season games, he's still sluggish outside the pocket, isn't good outside of structure and frequently takes too long to make throws that require timing and rhythm.

Glennon is a big guy with a big arm, which explains the NFL's infatuation with him, and his 30-15 touchdown-to-interception ratio looks impressive on the surface. However, the tape shows a veteran quarterback who must be managed far more than his salary would indicate.

Trubisky's physical upside is far more intriguing, and his development in the mental aspects of the game can best be worked out on the field. Trubisky and his coaching staff already appear aligned as to the best game plans in the short term, and even against better players and more advanced fronts and coverages, the boot-action/easy-reads strategy is a repeatable formula for success.

It will be up to Loggains to continue setting favorable schemes for his young quarterback, and for Trubisky to respond with obvious and quick growth. This isn't a team set to win the NFC North in 2017, so the best strategy is to let the kid take his lumps in live game action as soon as possible when the games matter.

Doug Farrar covers the NFL for Bleacher Report. Follow him on Twitter: @BR_DougFarrar.