The Ducks (18-12, 9-9 Pacific-10 Conference) finish the season tied for fifth in the conference and earned a first-round bye in the conference tournament.
Oregon's third consecutive win helped bolster its chances for a return to the NCAA Tournament, where the Ducks reached the final eight last season.
Arizona (18-13, 8-10), hoping to reach the NCAA Tournament for the 24th consecutive season, finishes in seventh place in the Pac-10.
It is the first time the Wildcats have finished with fewer than 11 Pac-10 wins since going 8-10 in 1983-84, which was Lute Olson's first season as coach. Olson is on a personal leave of absence this season.
Arizona cut its deficit to 70-65 with three-minutes left, but Maarty Leunen followed with a 3-pointer to start an 8-2 Oregon run to end the game and seal the win.
With Oregon trailing 46-42 early in the second half, Porter made three consecutive 3-pointers to ignite an 18-4 Ducks run. Hairston capped the run with a 3-pointer to put Oregon ahead 60-50 with 9:10 to play.
Porter had 11 points in the run, all in a span of 2:32. Oregon, feeding off the energy from its crowd in its home finale, led 7-2 early.
Arizona later went on a 16-6 run to take a 22-17 lead, capped by a three-point play by Nic Wise with 9:06 left in the first half.
Bayless, playing with five stitches under his right eye from a collision suffered Thursday, had 10 points in the first half.
Bayless, who entered as the Wildcats' leading scorer with 20.3 points per game, didn't play in Arizona's 84-74 loss to Oregon on Jan. 5.
Porter had 10 points in the first half, including a 3-pointer with six seconds remaining to bring Oregon within 38-35 at halftime.
The Ducks outrebounded the Wildcats 21-12 in the first half.
Oregon will open the Pac-10 tournament as the sixth seed and play No. 3 seed Washington State in the quarterfinals on Thursday. Arizona, the seventh seed, will play No. 10 seed Oregon State in the first round on Wednesday.