LAS VEGAS -- Arizona guard Nick Johnson scored 18 points and the Wildcats weathered a furious Colorado rally in the second half to beat the Buffaloes 79-69 Thursday in a Pac-12 tournament quarterfinal game.
Arizona (25-6) will play UCLA (24-8) in a semifinal game Friday at the MGM Grand Garden Arena. Colorado (21-11) will await its fate Sunday for the NCAA tournament.
Johnson, a sophomore, ended his personal slump against Colorado by making six of seven field goal attempts, including both attempts from three-point range. In his five previous games against the Buffaloes, Johnson made only 9-of-28 field goals, 4-of-22 from three-point range.
"I kept a positive frame of mind and believed in myself on the defensive end, and that opened things up on the offensive end," said Johnson, a significant reason why Colorado's Spencer Dinwiddie shot 4-of-12 from the field and was a non-factor in the first half.
Arizona led by as many as 14 points in the second half but Colorado trimmed the lead to 71-69 with 1:02 left behind Dinwiddie's 13 points after intermission.
"Our guys battled in the second half and showed the heart of a Colorado Buffalo and what that's about," Colorado coach Tad Boyle said. "These guys have more basketball ahead of them this year for the job they've done this season."
Johnson made a driving bank shot with 34.6 seconds remaining to put Arizona ahead 73-69, keeping it a two-possession game. Colorado's Andre Roberson missed on an aggressive move to the basket on the other end and was whistled for a foul on the rebound.
Arizona's Mark Lyons converted two free throws to put Arizona ahead 75-69 with 23.6 seconds left. After Johnson blocked a three-point attempt by Askia Booker, Arizona's Grant Jerrett corralled the rebound following another Booker missed three-pointer.
Jerrett was fouled and made two free throws to seal the game for Arizona.
"It seems like every time we get together with them, we play these very, physical, tough games, and today was no different," said Arizona coach Sean Miller, who evened his record against Colorado to 3-3 since the Buffaloes joined the Pac-12 last season.
A factor in the game was Colorado freshman center Josh Scott whistled for his second foul at the 14:53 mark in the first half and Arizona ahead 11-8.
Scott's backup, Shane Harris-Tunks, had his legs tangled with Arizona's Grant Jerrett, fell hard to the floor, heading his head, and had to be replaced by 6-foot-4 guard Sabatino Chen with 12:45 left. Colorado went with a small lineup of four guards and Roberson at power forward for most of the game.
Arizona attacked the lane and outscored Colorado 9-4 after the injury suffered by Harris-Tunks to build a 22-15 lead by the time Scott returned with 10:14 left in the half. Scott played only seven minutes in the first half. He finished with only two points and three rebounds in 22 minutes.
With Colorado lacking an inside presence, Arizona attacked the basket and drew fouls. The Buffaloes had four players with two fouls each at the half.
"It never helps when you bigs get in foul trouble, especially in a physical game," said Boyle, whose team trailed 39-28 at halftime.
Scott's foul trouble and Arizona's perimeter defense was difficult for the Buffaloes to overcome as Arizona set the tone in the first half. Colorado was 19-of-38 from three-point line in the two regular-season meetings between the teams but attempted only two from beyond the arc, making one, in the first half.
"We tried to be more aggressive on the ball screens and off the ball and worry more about our man and less about the help," Miller explained. "It's not always that you pitch a shutout defensively as much as how much your effort level can make the other team or other player work to score."
Despite Colorado's rally in the second half, the Buffaloes still shot worse (40.7 percent) in the second half than what they shot by halftime (45.8 percent). The Buffaloes managed only five three-pointers in 12 attempts.
"They just played solid defense," Dinwiddie said. "It wasn't nothing special. They did a great job team defensively the whole game. I don't what you want me to say to that."
NOTES: Colorado entered the game with a 3-2 edge over Arizona since joining the Pac-12 last season. The Buffaloes are 10-7 against the Wildcats overall, but 12 of those meetings were before 1975. ... Colorado was 5-0 in the Pac-12 tournament before Thursday's loss, having won the title in four games last season and the opener against Oregon State on Wednesday. ... Colorado practiced at the MGM Grand Garden Arena on Tuesday and played the Beavers on Wednesday. Arizona had not stepped into the arena until 30 minutes before Thursday's game.