Ohio State moved into second in the College Football Playoff rankings behind Alabama, with Michigan and Clemson still in the top four after losing for the first time this season.
Louisville was fifth and Washington dropped from fourth to sixth after its first loss.
"The margin of separation between teams two and six was very small," selection committee chairman Kirby Hocutt, who is also the athletic director at Texas Tech, said.
Clemson, Michigan and Washington - the Nos. 2, 3 and 4 teams in last week's rankings - all lost to unranked teams on Saturday. The Wolverines, who have three victories against teams in the selection committee's top 10, did not move after losing to Iowa. The Tigers ended up dropping two spots to No. 4 after losing to Pittsburgh.
Wisconsin was seventh and Penn State eighth, giving the Big Ten four teams in the top 10. Oklahoma was the highest rated Big 12 team at nine and Colorado was 10th.
THE OHIO STATE PROBLEM
Michigan's loss to Iowa created a potential predicament for the selection committee with the Buckeyes. Because Ohio State lost at eighth-ranked Penn State, the Nittany Lions would win a tiebreaker for the Big Ten East if both finish 8-1 in the conference, shutting out the Buckeyes from the conference championship game.
In two years of the playoff, all the participants have been conference champions and the committee is instructed to give some preference to league champs and head-to-head results when teams are similar.
There is little question that Ohio State would have the best overall resume in the Big Ten, and maybe one of the best resume's in the country, if it wins out. But would not winning the conference keep the Buckeyes out the way it did last season?
"We do not look forward and anticipate what may happen in the future," Hocutt said.
A Penn State loss in the next couple of weeks would clear things up, but the Nittany Lions play Rutgers on Saturday and finish at home against Michigan State. They will be heavy favorites in both games.
A possible solution for the Buckeyes and the selection committee: If Oklahoma wins the Big 12 and Wisconsin wins the Big Ten, the Buckeyes would have a victory over both. Problem solved.
If Penn State wins the Big Ten and the other Power Five conferences have champions with one-loss or less (i.e. Clemson in the ACC, Washington in the Pac-12, West Virginia in the Big 12 and Alabama in the SEC) we'll see just how much that conference championship is worth.
THE LOUISVILLE PROBLEM
The Cardinals' hurdle could be even more difficult to clear than the Buckeyes'. Without a Clemson loss at Wake Forest on Saturday, Louisville can't get to the ACC championship game because of its loss to the Tigers in early October.
Unlike the Buckeyes, who could have wins over Oklahoma, Wisconsin and Michigan, Louisville will put forth a resume that would include one marquee victory: a demolition of Florida State in September that might have been the most impressive performance of any team this season.
And having the likely Heisman Trophy winner in quarterback Lamar Jackson doesn't provide Louisville any bonus points from the committee.
We don't talk about individual players in that regard," Hocutt said.
A possible path the Cardinals: The Pac-12 picks itself apart and produces a champion with at least two losses and the Big 12 does the same. Even then Louisville might have to make a case against a Wisconsin team with a Big Ten championship and a victory against 16th-ranked LSU.
GROUP OF FIVE
No. 20 Boise State moved ahead of No. 21 Western Michigan in the rankings for the first time.
It is becoming fairly apparent that if there are no upsets in the next couple of weeks in the Mountain West, a championship game between two 11-1 teams, Boise State and San Diego State, could produce the team that earns the Cotton Bowl bid that will go to the best champion out of the Group of Five no matter what Western Michigan does.
If the Broncos stay unbeaten they would have a better chance to edge past the Aztecs, but they are not going to bump the Broncos from Boise.
Hocutt pointed out that Western Michigan has only one victory against an FBS team with a winning record while Boise State has a victory against No. 22 Washington State.