SEATTLE -- Stanford playing for the Pac-12 tournament title had become almost expected.
Twelve tournaments in conference history. Twelve times the Cardinal worked their way into the title game.
USC brought that streak to a thudding halt on Saturday night and potentially exposed some concerns for the fourth-ranked Cardinal heading into the NCAA tournament.
Cassie Harberts scored 10 straight points for USC in the final three minutes, and the Trojans held on in the closing seconds to upset No. 4 Stanford 72-68 in the Pac-12 tournament semifinals on Saturday night.
"Offensively we really struggled and that is something that I think we have two weeks to work on and that is our plan," Stanford coach Tara VanDerveer said. "This can be something hopefully that will get our collective team's attention."
USC will play for the championship and an automatic NCAA tournament bid on Sunday night against either Oregon State or Washington State. It will be the first time since the tournament's inception in 2002 that Stanford will not play in the championship game and will mark the Trojans' second appearance in the title game.
"We just beat a very good Stanford team and it demonstrates our growth. It doesn't demonstrate a weakness in Stanford," USC coach Cynthia Cooper-Dyke said. "And the strength of our conference, it demonstrates the strength of the Pac-12."
Chiney Ogwumike carried Stanford (29-3) with 30 points and 21 rebounds, but she was held scoreless for the final 7 minutes and her supporting cast was not able to counter Harberts' late outburst for the Trojans.
Lili Thompson finished with 13 points and Amber Orrange added 11, but the Cardinal were 4 of 14 from 3-point range and shot 32 percent overall.
"I think that sometimes it's almost like your strength is your weakness. We go inside to Chiney and she delivered for us so well. But we have to have other people stepping up or being offensive contributors," VanDerveer said. "We did not shoot the ball well. We were not moving the ball well. ... The last maybe month or so we've been really stagnant offensively and we need to really fix that."
Ogwumike moved into a tie as the Pac-12 career scoring leader in defeat. She tied Candice Wiggins' mark of 2,629 points with a pair of free throws with 7:09 left, but went scoreless the rest of the way.
"I missed a couple of shots. I was still being aggressive," Ogwumike said. "I honestly don't think there was a change. We just need to finish better."
Harberts' scoring run came after Stanford had rallied from a 10-point deficit to take a 60-57 lead with 5:06 remaining. Harberts finished with 13 points. Alexyz Vaioletama led USC (21-12) with 19 points.
Ariya Crook added 15 points for the Trojans and Vaioletama added 15 rebounds to go along with her scoring that was 11 points more than her season average.
Stanford missed 13 of 14 shots to start the second half and was down 46-36 before Ogwumike's rebound putback with 12:55 left. That was the start of her takeover. She converted a three-point play to get Stanford within seven, then blocked Crook's layup. The block eventually led to Orrange's 3-pointer from the top of the key. Ogwumike added a pair of free throws and the Trojans lead was down to 50-48.
The run continued with six more points from Ogwumike and Stanford retook the lead on Thompson's driving layup for a 58-57 lead with 6:45 left. Free throws from Thompson pushed the lead to three.
The Trojans pulled even at 60 on Harberts' three-point play with 3:07 left. She added two more jumpers and another three-point play for a 67-60 with 1:23 remaining.
Thompson scored in the lane with 27.6 left and USC's lead was down to 68-66. Crook was fouled and hit two free throws a 70-66 lead. Orrange hit two free throws of her own and Brianna Barrett split a pair for a 71-68 lead.
Instead of extending the game, Stanford tried to get look at a tying 3-pointer, but Ogwumike's rushed attempt was off and Barrett's free throw with 1 second left clinched the victory for USC.