Mark Lyons poured in a game-high 24 points to lead third-ranked Arizona to a 92-83 overtime win over Colorado on Thursday.
The Wildcats (13-0, 1-0 Pac-12) trailed 56-40 with just under 13 minutes left in the second half, but were able to cut it to 68-61 following a Lyons trey with just over four minutes remaining.
The Buffaloes (10-3, 0-1) were able to push their spread back to 77-68 with 1:49 remaining, but a 10-3 Arizona push made it a two-point game with 33 ticks showing.
The Wildcats fouled Jeremy Adams on the inbounds pass, and Adams missed the subsequent free throws to keep Arizona's hopes alive.
Lyons was fouled with 10 seconds left and buried a pair from the charity stripe to knot things up at 80-80.
Colorado's Sabatino Chen took the ball at the top of the key as the clock wound down, shook a defender with a pair of crossovers, then banked home a 3- pointer as the buzzer sounded.
An official, however, determined that the ball was in contact with Chen's fingertips as the final horn sounded, and the shot was waved off.
Colorado head coach Tad Boyle voiced his displeasure about the decision, saying he was "sick to my stomach" after seeing the replay.
"I think our team deserved to win that game, but we didn't, and we have to move on from it," Boyle added.
Colorado scored just three points in the bonus period as the Wildcats improved to 13-0 when opening Pac-12 play at home.
Kevin Parrom scored 16 points and pulled down eight rebounds and Nick Johnson added 12 points, five boards and three steals for the Wildcats.
"We would have gotten what we deserved if we had lost," Arizona head coach Sean Miller said. "They outplayed us for a majority of the game."
Askia Booker led the Buffs with 18 points and Chen finished with 15 points off the bench.
Colorado led 21-7 just past the midway point of the first half before pushing it to 34-21 with 1:43 left. Arizona, though, scored the final six points of the half to go into the break trailing 34-27.
Six Arizona players finished with double-figure scoring efforts. Solomon Hill had 15 while Grant Jerrett and Kaleb Tarczewski added 10 points apiece ... The Wildcats have won five of the last eight meetings between the two schools.