For the first time all season, there is a change at No. 1 in the latest Associated Press men's basketball poll.

Duke jumped all the way to the top spot after an upset win over previously unbeaten Gonzaga, while losses by UCLA and Kansas helped shake up the entire top five.

The nation's best teams are getting tested right away with high-profile games, and it has created some early separation near the top of the rankings. Here is the latest Top 25 heading into Week 4 of the season.

AP Poll

1. Duke

2. Purdue

3. Gonzaga

4. Baylor

5. UCLA

6. Villanova

7. Texas

8. Kansas

9. Kentucky

10. Arkansas

11. Arizona

12. BYU

13. Tennessee

14. Florida

15. Houston

16. Alabama

17. Connecticut

18. Memphis

19. Iowa State

20. USC

21. Auburn

22. Michigan State

23. Wisconsin

24. Michigan

25. Seton Hall

It was a busy week for Gonzaga, which went from being dominant against UCLA to suffering its first loss to Duke.

The Bulldogs cruised to an 83-63 win last Tuesday in what was a battle of the top two teams in the rankings. The defense was incredible in the win, holding the Bruins to just 34.8 percent shooting from the field and 2-of-12 from three-point range.

UCLA followed it up with a win over UNLV to improve to 6-1 but still dropped to No. 5 in the latest poll.

Gonzaga, meanwhile, fell to 6-1 and No. 3 after suffering an 84-81 loss to Duke in what could be the best game that fans see all season.

Paolo Banchero starred in the first half before dealing with cramps in the second, but he still outdueled fellow top prospect Chet Holmgren. 

With Mark Williams coming through with 17 points, nine rebounds and five blocks, Duke was able to pull out the impressive victory to improve to 7-0 on the season.

This wasn't the only upset of the week, however, as Kansas fell from No. 4 to No. 8 after a 74-73 loss to Dayton at the buzzer.

Dayton overcame 20 turnovers to pull the upset, creating doubts about Kansas after its quiet start to the season.

Memphis suffered its first loss of the season this week as Iowa State earned an easy 78-59 blowout win. Gabe Kalscheur scored 30 in the win to cap a big week for the Cyclones (6-0) after also beating Xavier.

Baylor (7-0) avoided the same fate, winning the Battle 4 Atlantis with wins over Arizona State, VCU and Michigan State. Despite significant turnover from last year's NCAA championship squad, this team is clearly a top contender once again in 2021-22.

Purdue (6-0) wasn't challenged last week with just a blowout win over Omaha, but upcoming matchups with Florida State and Iowa will represent tougher tests for the squad.