After an eventful fourth week across the country, there was major restructuring in the Associated Press Top 25 poll.

The top half of the rankings remained largely unchanged thanks to the lack of major upsets. Texas defended the top spot after a 51-3 win over Louisiana-Monroe and with No. 2 Georgia having a bye. Ohio State and Ole Miss, ranked third and fifth, also had clear wins, but in Ole Miss’ case, it wasn’t enough to maintain a spot in the top five.

No. 11 USC was the highest-ranked team to go down. The Trojans fought their way to a lead against Michigan after a sloppy start in the fourth quarter before the Wolverines embarked on a 10-play, 89-yard run that culminated in Kalel Mullings’ touchdown run with 37 seconds left.

Only time will tell how much the result will affect both teams.

Michigan quarterback Alex Orji attempted 12 passes and gained 32 yards through the air. The Wolverines may not be as successful on the ground — they ran for 291 yards as a team — when opponents no longer have to respect Orji as much as a thrower.

At USC, enthusiasm for improvements on defense waned somewhat as the Trojans were unable to stop Michigan on the game’s decisive drive. Overall, they do not look like serious title contenders in Lincoln Riley’s third season as head coach.

The same goes for Oklahoma with Brent Venables at the helm. Venables may be a brilliant defensive coach, but the substitution of quarterback Jackson Arnold in the middle of the game against Tennessee may indicate bigger problems.

It would not reflect well on the coach if he cannot develop Arnold further, 5-star recruit came out of high school and also missed the hiring of Seth Littrell as offensive coordinator.

It didn’t help Sooners fans that Venables was trumped as coach by Josh Heupel at the OU legend’s home game.

The win was a strong statement from the Vols, who had made noise in their three previous games but were not seriously challenged in those games. Saturday showed that they can step up the defense when needed and pull off ugly wins.

Tennessee took a step back in 2023, finishing with two fewer wins than the previous year. Now Heupel has brought the program back among the best in the FBS.

Michigan and Tennessee’s victories were the headlines of week four, but they weren’t the only important matchups.

Illinois beat Nebraska in overtime on the road on Friday night to solidify its position in the Top 25. The Cornhuskers were knocked out of the AP poll. Utah held off Oklahoma State’s late comeback attempt to earn a key road win without starting quarterback Cam Rising. Kansas State (No. 13) and Northern Illinois (No. 23) were both beaten by unranked teams.

AP voters have had to deal with all the consequences, and their task won’t get any easier in Week 5.

Alabama faces its first challenge of the Kalen DeBoer era when it hosts Georgia in Tuscaloosa. Penn State hosts the Fighting Illini in Happy Valley. Louisville hosts Notre Dame on the road, with the Fighting Irish offense still struggling with Riley Leonard at quarterback. Oklahoma State and Kansas State meet in a matchup of Big 12 teams all in need of a win.

No matter how things turn out, there is sure to be big movement in the AP poll next week.