With conference play in full swing, it was another hectic week for the nation's best teams, leading to several shake-ups in this week's top 25 as another unbeaten fell. 

A new No. 1 

For the first time since Dec. 5, there is a new top-ranked team in men's college basketball. Then-No. 18 Butler upset then-No. 1 Villanova 66-58 Wednesday at historic Hinkle Fieldhouse in Indianapolis, holding National Player of the Year candidate Josh Hart to 3-of-11 shooting to end the Wildcats' 20-game winning streak dating back to last season. Butler had four players in double figures to pull off the upset and rose to No. 12 this week, and Villanova fell to No. 3 following its first loss in almost 10 months.

With the Wildcats' loss, Baylor surged to the top of the poll for the first time in school history. The Bears improved to 14-0 with two narrow home wins against Iowa State and Oklahoma State last week, but will have to defend their new status with a road test at No. 10 West Virginia Tuesday night. Baylor and No. 5 Gonzaga are now the only undefeated teams left in the nation.

Top-10 showdown coming up for Duke

West Virginia was ranked seventh last week before falling in overtime 77-76 at Texas Tech on a late Anthony Livingston 3-pointer. The Mountaineers' second loss of the season allowed the Blue Devils to move up to No. 7 this week after being ranked eighth a week ago. 

Like West Virginia, Duke will face its toughest ACC test of the season Tuesday night when the Blue Devils take on No. 9 Florida State. The Seminoles moved into the top 10 for the first time this year after routing then-No. 21 Virginia Tech 93-78 Saturday in their only game last week and getting help from other ACC contenders that lost Wednesday.

ACC chaos

Then-No. 9 Louisville fell 77-70 at then-No. 23 Notre Dame, as the Fighting Irish got 24 points from sharpshooter Steve Vasturia and showed they have the toughness to hang with the physical Cardinals. On the same night, then-No. 11 Virginia lost 88-76 in overtime at Pittsburgh, as the Panthers used a barrage of 3-pointers early in the extra session to put away the Cavaliers, who forced overtime on a deep triple from point guard London Perrantes. 

As a result of the ACC madness, Duke now leads the ACC's ranked teams, followed closely by the Seminoles, North Carolina at No. 12—the Tar Heels held off Clemson in overtime on the road before routing N.C. State last week—Louisville at No. 14, Virginia at No. 19 and Notre Dame at No. 20. Virginia Tech fell out of the poll a week after its upset of Duke, as the Hokies got blown out by both N.C. State and Florida State. 

With the Blue Devils taking on Florida State and Louisville on the road this week and the Seminoles battling North Carolina as well, expect more ACC shake-ups next week and throughout the rest of a brutal league slate. 

No unbeatens left in Big Ten play

After just two weeks, no Big Ten team is unbeaten in conference play, making the league the only major conference without an undefeated team against conference opponents. Then-No. 20 Purdue snapped then-No. 13 Wisconsin's nine-game winning streak with a decisive 66-55 win Sunday powered by big man Caleb Swanigan's 18 points and 13 rebounds. The result means there are six teams with one loss atop the conference standings since Minnesota upset the Boilermakers Jan. 1.

The Golden Gophers moved into the top 25 for the first time this season this week after two more wins last week, and will look to avenge a one-point loss to Michigan State Dec. 27 when the teams meet again Wednesday. 

Following its third straight defeat to Wisconsin 75-68 at home Tuesday, Indiana fell out of the rankings this week. The Hoosiers were still ranked last week thanks to early-season wins against Kansas and North Carolina, but now have five losses. The ranked Big Ten teams are now No. 17 Purdue, No. 18 Wisconsin and No. 24 Minnesota, though as is the case with the ACC, more chaos is likely on the way.