Maggie Lucas scored 21 points and No. 8 Penn State clamped down on Iowa in the second half to earn an 81-69 win on Thursday night.
Ariel Edwards scored 15 points off the bench and Alex Bentley added 14 points for the Lady Lions (21-3, 11-1 Big Ten), who have won 15 of their last 16 games.
Morgan Johnson had 17 points and 11 rebounds for Iowa (16-10, 5-7) in tying a school record with her 121st career start.
The Hawkeyes have lost five straight, but this was their first loss to a ranked opponent in seven games. The six wins against ranked teams are the most in the nation.
The Hawkeyes hit only one field goal during a nearly eight-minute stretch in the second half as their 38-37 lead turned into a 12-pont deficit after Lucas hit a 3-pointer.
Lucas hit a pretty step-back jumper with 12 minutes left to push Penn State's lead up to double digits for the first time.
Iowa finally shook its shooting slump, but Lucas and the Lady Lions always had an answer.
After the Hawkeyes hit a pair of free throws for their first points in 4½ minutes, Lucas knocked down a 3-pointer on the other end.
Theairra Taylor's layup gave Iowa only its second field goal in nearly eight minutes, but Lucas responded with a tough drive of her own, earning and converting two free throws.
The Hawkeyes led the Big Ten in free-throw percentage, but made only 11 of 19 against Penn State. They also missed on the front-end of a pair of one-and-ones in the first half.
Iowa's Jamie Printy, who averages 14 points a game, missed all five of her field goal attempts, finishing with two points.
Reserve guard Melissa Dixon scored 16 points for Iowa on 4 of 9 3-point shooting.
Both teams looked tight in a sloppy first half that produced 22 turnovers and 20 fouls.
Neither team could pull away early — there were seven ties and eight lead changes in the first half. When Penn State went on a 12-5 run midway through the half to take control, the Hawkeyes responded with a 9-2 burst to close the lead.
Iowa had an opportunity to tie it before halftime, but a blown layup turned into an open transition 3-pointer from Lucas that gave the Lady Lions a 37-34 lead at the break.