A narrow victory over Purdue was not enough to keep Michigan State the No. 2 team in the country.
The Spartans dropped two spots, down from No. 2 to No. 4, when the latest AP poll was released Sunday.
Still, Michigan State remained in position for a shot at a spot in the College Football Playoff, one of five Big Ten teams ranked in this week's top 25.
The Spartans scored a big win over Oregon in Week 2 that bounced them up to the No. 2 spot, but things haven't exactly been smooth sailing since. Saturday, Michigan State led Purdue, 21-0, at halftime only for Purdue to come back and force the Spartans to sweat out a 24-21 finish.
[MORE BIG TEN: Spartans survive late Purdue comeback to stay undefeated]
Ohio State has struggled lately, too, finding it quite difficult to get the quarterback position going. And the Buckeyes also had a narrow win Saturday, beating Indiana by just a touchdown, 34-27. Ezekiel Elliott rushed for a career-high 274 yards and a trio of touchdowns in a performance that got his name back into the Heisman discussion.
Northwestern, thanks to a blowout 27-0 win over Minnesota, moved up three spots from No. 16 to No. 13. Michigan, thanks to a second straight shutout win, this one 28-0 over Maryland, moved up four spots from No. 22 to No. 18. This sets up a top-20 showdown between the Cats and Wolverines this week in Ann Arbor.
Iowa, still undefeated after a 10-6 win over Wisconsin, entered the top 25 at No. 22, the Hawkeyes' first appearance in the rankings since 2010.
The Badgers fell out of the top 25.