Wisconsin (10-5 Big Ten, 17-7 overall) is riding a six-game conference winning streak for the first time since 1951.
Duany Duany hit two straight 3-point baskets to cap a 13-3 Wisconsin run to tie the game, 36-36, with just under nine minutes remaining.
Calderwood pulled the Badgers to within two points on a driving layup with 17.2 seconds remaining.
Wisconsin got the ball back with 14.8 seconds left on Iowa's inbounds play under the Badger basket, as the ball came loose and Mike Kosolcharoen dove to get it, then called timeout.
Iowa (9-6, 18-9) had one last chance to win the game, but Andre Woolridge's last-second shot bounced off the rim. Woolridge led the Hawkeyes with 17 points.
Michigan State 67, Ohio State 65
Jason Klein's only shot of the second half, a 3-pointer with 47 seconds left, provided the winning basket as Michigan State beat Ohio State 67-65 last night.
The loss doomed Ohio State (5-10, 10-14) to its fourth straight losing season - the first time that's happened in the school's 98 years of the sport.
Klein, who finished with 13 points, hit his big bucket after taking a pass from Thomas Kelley, who passed the ball out while driving the lane.
Antonio Smith later added a free throw, with Ohio State's Damon Stringer closing the scoring with a 50-foot 3-pointer at the final buzzer.
Ray Weathers led the Spartans (7-8, 14-10) with 21 points, hitting 8 of 12 shots from the field including 5-of-8 3-pointers.
The win assured Michigan State of a winning record, and improved the Spartans' chances of an NIT bid.
Purdue 72, Northwestern 61
Chad Austin scored 20 points and Jaraan Cornell added 15 to give Purdue its third straight victory last night, a 72-61 decision over Northwestern.
The victory kept the Boilermakers in second place in the Big Ten, a half-game ahead of Wisconsin.
Northwestern (2-14, 7-20) fought back to tie the game at 52 and again at 54.
But a pair of free throws by Mike Robinson sparked an 8-0 Purdue run, and the Boilermakers (11-5, 16-10) sank 10 of 12 free throws in the final 2:02 to seal the victory.
The Boilermakers, who entered the game averaging 43 percent from the floor, shot just 36 percent (9 of 25) in the first half.