The Lady Lions then turned to Lucas, who made consecutive 3-pointers to trim Michigan State's lead to one. Penn State had a couple of chances to move in front but Alex Bentley missed a jumper and Mia Nickson was off on a layup attempt.
That provided an opening for the Spartans, who put the game away with a 10-0 burst. Thomas' layup made it 44-33 with 4:08 left, leading to a celebration on Michigan State's sideline and a timeout by Penn State.
"They played good defense," said Bentley, who was 3 for 15 from the field. "They tried to stop us from getting in the lane. They forced us to go into the baseline. We just couldn't get our offense going."
Penn State got off to a fast start then struggled to score in an ugly first half that featured more turnovers (14) than field goals (11).
Tori Waldner converted a layup with 12:41 to go to give the Lady Lions a 16-5 lead — but that was their last basket of the period.
Penn State staggered into the break with a 19-17 lead despite shooting 20 percent (6 for 30) and losing 28-21 in the rebounding battle. That's because Michigan State was even worse, shooting 18.5 percent (5 for 27) and committing nine turnovers.
Led by Thomas, the Spartans eventually calmed down and shot 60 percent (15 for 25) in the second half of their first victory against a top-10 team this season.
"Jasmine went to a point guard school one summer and she came back with a lot of notes and one of the things she told me she learned there was be the face your team needs to see," Merchant said. "She always kind of refers back to that."
It served her well on Saturday.
Jay Cohen can be reached at http://www.twitter.com/jcohenap