The Wildcats improve to 22-6 overall and 12-3 in the Pac-12, continuing to hold a two-game lead in the loss column atop the Pac-12 standings.
While they got their third straight win, life without Trier proved to be tenuous.
The Beavers led 61-59 with 2:01 left in regulation, and Ethan Thompson and Stephen Thompson Jr. both missed wide-open corner 3s that could have buried Arizona.
One of those misses came with 22 seconds left, and Rawle Alkins corralled the rebound and drew a foul on UA’s next possession.
The sophomore would knock down two free throws to tie the game, and Thompson Jr.’s ensuing jumper at the buzzer was off the mark, sending the game into overtime.
Arizona outscored OSU 14-4 in the overtime period. Alkins, who had 16 points and struggled for most of the game, knocked down two clutch 3s, propelling the Wildcats to victory.
Deandre Ayton finished 19 points and 12 rebounds, while Dusan Ristic chipped in with 14 points before fouling out in overtime.
Ristic has now won 110 games at Arizona, tied with Kaleb Tarczewski and Matt Muehlebach for the most in program history.
The Trier-less Wildcats struggled offensively for the most part, averaging just a hair over one point per possession. They shot 48 percent from the field and 5-of-16 from 3.
Oregon State was worse, though, shooting just 40 percent.
The Beavers actually went the final 9:08 of regulation without a bucket, but made plenty of trips to the free throw line to keep them in the game.
They were 14-of-17 from the stripe, while Arizona uncharacteristically clanked several, shooting just 16-of-24.
With a revamped starting lineup, Arizona looked rattled to start the game, falling behind 8-3 in front of the orange-clad crowd. The Wildcats’ first offensive possession was an airball from Trier’s replacement, Dylan Smith, who finished with just three points.
But Arizona quickly sorted things out, and nine Wildcats scored in the first half as they took a 37-29 lead into the locker room.
Arizona, which was also without Ira Lee who did not travel because of a concussion, got 14 points from its bench. Emmanuel Akot, Brandon Randolph, and Alex Barcello each scored four points.
It was Barcello’s first appearance since Jan. 31’s win at Washington State.
Ristic was the only Wildcat to score in double figures in the first half, tallying 10 of his 14 points in that period.
The big man hit a 3 to put Arizona up 25-15, then hit a jumper from the elbow to extend the lead to 27-15 with 7:15 left. That was UA’s largest lead of the game.
Oregon State shot 50 percent in the first 20 minutes but also committed 10 turnovers, and eventually finished with 16. Ethan Thompson had 11 first-half points, including three 3s, and finished with a game-high 20 when all was said and done.
Arizona relied heavily on Ayton in the second half. The 7-footer scored 15 of his 19 points in the second half plus overtime.
The Wildcats held a narrow lead until Gligorije Rakocevic made a hook shot to tie the game at 50 with 9:51 left.
Then Thompson Jr. hitter a runner to give Oregon State the lead as Arizona went over four minutes without a field goal.
Alkins finally snapped that skid, scoring inside to help UA re-take a 53-52. There would be a few more lead changes, as both teams struggled offensively in the second half.
Arizona shot 35 percent in the period; OSU shot 38 percent.
Parker Jackson-Cartwright, who had nine points, made a floater with 3:30 left to put Arizona up 59-58, but OSU grabbed a 61-59 lead after three free throws.
That was the score when Alkins stepped the line with 14 seconds left with a chance to tie the game. He was just 4-of-8 at the stripe until that moment, but knocked down both despite OSU coach Wayne Tinkle calling a timeout after the first make.
Arizona is now 9-0 when it has blown a double-digit lead this season, as it continues to find a way to win tight games.
The Wildcats have never swept the Oregon schools on the road under Sean Miller, but they will have a chance to do so Saturday in Eugene against the Ducks.
And they will likely have to do it without Trier, who was declared ineligible by the NCAA on Thursday after testing positive for a banned substance.
When asked about Trier’s status after the game, Miller simply said “I’m good” before storming off.
Follow Ryan Kelapire on Twitter at @RKelapire