LAS VEGAS — Colorado had seen Arizona’s defense at work before, in person and in the Pac-12 tournament quarterfinals.

Even knowing what was coming, the Buffaloes didn’t stand much of a chance.

Unable to match Arizona after a close first half, Colorado lost to the fourth-ranked Wildcats 63-43 in the Pac-12 semifinals on Friday night.

“We knew they were good defensively and we knew we were going to have to make some shots to beat them. We couldn’t get going,” Colorado coach Tad Boyle said. “Their defense had something to do with that. Our offense had something to do with that.”

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Arizona (30-3) crushed Utah in its tournament opener behind a record-setting defensive show.

The Wildcats didn’t peel open the record book against Colorado, but they sure gave the Buffaloes fits.

Unlike its previous win over Colorado, Arizona started slow, allowing the Buffaloes to keep it close at halftime.

Once they got rolling, Colorado had no answer for the Wildcats’ defensive pressure and string of highlight-reel plays that had MGM Grand Garden Arena feeling like McKale Center West.

Arizona shot 60 percent in the second half and held Colorado (23-11) to 5-of-22 shooting in the final 20 minutes to earn a spot in Saturday’s championship game against UCLA.

Nick Johnson scored 16 points for Arizona. T.J. McConnell facilitated the Wildcats’ offense with 12 points, five assists and four rebounds.

“Our defense became great in the second half, but our offense found its flow,” Arizona coach Sean Miller said.

Colorado was able to hang with Arizona behind its defense in the first half.

But playing their third game in as many days took its toll on the Buffaloes in the second half and they had no pushback when the Wildcats started to race away.

Askia Booker had 20 points to lead Colorado.

Now the Buffaloes have a two-day wait to see if the NCAA tournament selection committee deems them worthy of the bracket.

UCLA rolls

Norman Powell scored 22 points, Travis Wear added 16 and UCLA started its rout of Stanford early, rolling over the Cardinal 84-59 in the other Pac-12 semifinal.

Coming off a rout of Oregon in the quarterfinals, UCLA (25-8) started another one by building a 12-point lead in the opening four minutes.

The Bruins kept making shots and kept building the lead.

Kyle Anderson added 13 points, eight rebounds and seven assists for UCLA, which shot 65 percent.

Stanford (21-12) was listless from the start of its third game in three days, unable to match UCLA’s intensity or athleticism.

The Cardinal labored offensively and barely got in the Bruins’ way on defense, and are left now to wait for Selection Sunday to see if they’ll be in the NCAA tournament.

Dwight Powell scored 16 points and Chasson Randle added 11 for Stanford.