LAS VEGAS —  Oregon missed 21 shots in the first half, many of them right at the rim.

Then Louis King opened up the second half with a tip-in before Payton Pritchard drove to the hoop for consecutive baskets and Utah’s six-point lead was gone.

“That got the energy level up and it was game on,” Oregon men's basketball coach Dana Altman said.

The sixth-seeded Ducks relied on their defense to keep them in the game once again until their offense came along in the second half to rally for a 66-54 win over third-seeded Utah on Thursday night in the quarterfinals of the Pac-12 Tournament at T-Mobile Arena.

Oregon (21-12) will face No. 2 seed Arizona State (22-9) in the semifinals at 8:30 p.m. Friday.

“We can’t afford to come out in the first half again and have less energy,” said King, who scored 20 points. “We came back in the second half and were active on defense, got easy baskets in transition and that led to the win.”

Oregon was 8-for-29 from the field in the first half to fall behind 24-18.

“In the first half, our defense kept us in it so as poorly as we played on offense, we were still in the game,” Altman said.

Pritchard got another steal and layup to tie the game 28-28 before adding a layup and free throw that put Oregon up for good as he let out a loud scream to the crowd.

“Having emotion like that can get the team fired up and bring more defensive energy,” said Pritchard, who also finished with 20 points. “That’s all I was trying to do.”

Oregon led 41-36 before King added a basket and Victor Bailey got a layup to push the margin to 45-36. When Utah closed within 47-43, Paul White hit a 3-pointer to begin a stretch of five straight possessions with points for the Ducks, including a couple of alley-oop dunks for Kenny Wooten that stretched the lead to 58-49 before Oregon sealed the win with free throws.

“Our ball movement and the ability to attack the rim and get to the basket was better in the second half,” Altman said. “We worked hard on defense in both halves.”

Francis Okoro tied the tournament record with six blocked shots as Oregon held a sixth straight opponent below 62 points. Utah, which shot 37.8 percent on 3-pointers in the regular season, was 2-for-23 from behind the arc.

“They missed some open 3s, but I thought a lot of them were contested as we wanted to run them off the line,” Altman said.

Oregon’s only lead of the first half was 14-13 when Ehab Amin made a 3-pointer with 8:33 left, but the Ducks added only four more points the rest of the half.

Oregon needed less than 10 minutes in the second half to match its first-half point total. The Ducks were 17-for-28 from the field in the second half.

“Our ball movement got better and we were getting layups and attacking their bigs on the ball screens,” said Pritchard, who had 16 points in the second half. “It was two different halves and obviously this team is capable of a lot as we showed in the second half. That is how we have to bring it from the tip tomorrow.”