HOFFMAN ESTATES, Ill. (AP) -- Jasmine Thomas remained calm when Michigan State charged into the lead. She had that same relaxed expression when Penn State rallied, and she remained composed as she dribbled out the final seconds of an impressive victory.
Thanks to Thomas' steady presence and a stout defense, the Spartans upset the eighth-ranked Lady Lions 54-46 in the Big Ten tournament semifinals Saturday.
''It's a 40-minute game and Penn State is the type of team that can get going instantly,'' said Thomas, who scored 14 of her 19 points in the second half. ''There's no time to celebrate, you've got to stay in the game, stay in the moment.''
Becca Mills added 16 points for Michigan State (24-7), which held Penn State to 22 percent shooting. Jasmine Hines had 14 rebounds, helping the Spartans to a 52-38 edge on the glass.
Michigan State allowed just 51.4 points per game during the regular season, tops in the Big Ten. It was the lowest scoring total and shooting percentage this year for Penn State, which posted two convincing victories over the Spartans on its way to the conference title.
''We rely on our defense,'' Michigan State coach Suzy Merchant said, ''so to see our defense come to fruition tonight, I'm very, very proud of them and feel good about the win.''
Michigan State will meet third-seeded Purdue in the title game Sunday. The Spartans split their two regular-season games against the Boilermakers, losing 67-62 in overtime on Jan. 27 and winning 68-61 at Purdue on Feb. 28.
The Boilermakers advanced with a 77-64 victory over No. 21 Nebraska in the first semifinal.
Penn State (25-5) won the regular-season championship and lost in the tournament semifinals for the second straight year. The Lady Lions fell 68-66 against eventual champion Purdue in 2012.
Maggie Lucas, the conference player of the year, had 23 points and nine rebounds, but she was the only one to score in double figures for the Lady Lions.
''We didn't shoot the ball well at all,'' coach Coquese Washington said. ''They shot the ball much better than we did. We had too many stretches where we got pretty decent looks that didn't go down.''
Penn State led 21-17 early in the second half before the Spartans responded with a 15-3 run. Mills made a 3-pointer before Courtney Schiffauer converted a layup to give Michigan State its first lead of the game. Mills tacked on two more jumpers and Thomas' basket made it 32-24 with 10:54 remaining.
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 https://www.twitter.com/jcohenap