Arizona had won its opening 14 contests, but wasted a hot start against the Ducks. The Wildcats scored the first 11 points of the game, then melted under Oregon's defensive pressure and were outscored during the remainder of the opening period 41-19.
The Wildcats' loss left Duke and Michigan -- ranked No. 1 and 2 in the country -- as the only unbeaten teams in major college basketball.
Arizona closed within three points on a 3-pointer by Nick Johnson with 52 seconds remaining and the Wildcats got the ball back with a chance to tie the game.
Johnathan Loyd, however, stole the ball from Arizona's Nick Johnson and Loyd made 1-of-2 free throws with 10 seconds to wrap up the victory.
Singler scored 14 points and had eight rebounds to go with seven assists. Tony Woods, Carlos Emory and Dominic Artis all had 10 points for the Ducks (13-2, 2-0 Pacific-12 Conference).
Arizona, which slipped to 2-1 in league play, was led by the 21 points of Mark Lyons.