TEMPE, Ariz. -- Oklahoma State looked lost for a half without the nation's No. 3 scorer Andrea Riley.
Then Toni Young and Tegan Cunningham took over as the Cowgirls used a fierce fullcourt press to get back in the game.
Young scored 16 of her career-high 22 points in the second half and fourth-seeded Oklahoma State rallied from an 18-point halftime deficit to beat No. 13-seed Chattanooga 70-63 in the first round of the NCAA women's tournament on Saturday night.
"Wow, I've been in this a long time now, and I think it's the greatest win I've ever been associated with," Oklahoma State coach Kurt Budke said. "It's one thing to come back and get a win, but it's another thing to get your butt beat for 20 minutes and figure out a way to come back without your star."
Riley was suspended by the NCAA for the game because she hit an opponent in the back of the head in the first round two years ago.
Cunningham, who made 1 of 13 shots in the first half, scored 19 of her 25 points in the second for Oklahoma State (24-10), which outscored the Lady Mocs 51-26 after the break after scoring a season-low 19 in the first 20 minutes. Senior Ally Clardy, Riley's roommate and her replacement most of the game, had 10 assists.
"We went from a story that people were questioning to I think the greatest story in America right now in women's college basketball after this game," Budke said. "... I thought it showed unbelievable heart from this team."
Kayla Christopher scored 15 and Shanara Hollinquest 14 for Chattanooga (24-9).
"It hurts a lot," Hollinquest said. "It was right there in our fingertips and we let it go."
Riley, a senior who averaged 26.6 points per game, cheered on the Cowgirls from two rows behind the team bench as frustrated Chattanooga committed 17 second-half turnovers. She went from visions of an ugly end to her college career to knowing she will play at least one more game.
"She's my roommate, my friend for four years," Clardy said. "It would kill me, absolutely kill me, to play my last game without her."
Oklahoma State plays Monday night against Georgia. The school wouldn't let Riley talk to reporters after the game.
According to STATS, it was the biggest halftime comeback since 1999, besting the previous mark of 12.
Talk about a transformation.
The Cowgirls shot 17 percent (6 of 35) in the first half, 60 percent (21 of 35) in the second. They never made a 3-pointer, going 0 for 15, but they got back into it with layups and short jumpers.
"Everyone on the court said just keep on shooting," Cunningham said. "Everyone had faith in me and I just had to keep on shooting. I knew eventually they'd start falling."
Riley has scored 37 percent of Oklahoma State's points this season, along with an average of 6.5 assists per game, and her teammates obviously were pressing from the start to try to make up for her absence.
In one stretch, the Cowgirls missed 15 shots in a row, as Chattanooga took a 29-10 lead on Christopher's 3-pointer with 9:53 left in the half.
The Lady Mocs made their first five shots, three of them 3-pointers, then they turned as cold as the Cowgirls, going seven minutes without a point. Still, an 18-point lead had to feel comfortable. Oklahoma State's 19 first-half points were the lowest scoring in the tournament.
Then came that nasty press.
"The funny thing is we barely practice the press," Clardy said. "I honestly don't know if I've practiced the press all year. We just threw it out there. All it is, is heart. Defense is heart, so we went after it."
The Cowgirls erased the 18-point lead in less than 11 minutes.
Chattanooga turned it over three straight times in the first 2:24 of the second half. With 11:11 to play, the Lady Mocs had far more turnovers (11) than they did points (six) in the second half.
Precious Robinson's layup finally tied it at 48-48 with 9:09 to play and Oklahoma State took the lead on Megan Byford's two free throws with 7:47 to go.
Cunningham's jumper put the Cowgirls up 60-53 with 5:04 to go, then the Southern Conference champs managed one last gasp.
Michelle Davis made a 3-pointer and Hollinquest a layup that cut it to 62-61 with 3:20 to go, but Oklahoma State forced two more turnovers and outscored the Lady Mocs 9-2 the rest of the way.
"You've got to give Oklahoma State a lot of credit," Chattanooga coach Wes Moore said. "It was a great move going to the press and falling back into the zone."
The Lady Mocs are 1-10 in NCAA tournament games.