The Trojans (13-6, 4-3 Pac-10) were nearly perfect in the overtime session, going 5-for-5 from the field -- all 3-pointers -- and 6-for-8 from the free-throw line as they quickly broke away from the 74-all tie.
It was the fourth straight win for USC, while the Ducks (12-8, 3-5) have now lost four straight since upsetting then-No. 23 Stanford two weeks ago.
It was Mayo's first game since the NCAA ruled on Friday the superstar freshman had violated rules by accepting free tickets from Denver Nuggets forward Carmelo Anthony to an NBA game. Mayo's punishment didn't include any missed games, but he had to contribute $460 -- the total value of the two tickets -- to a charitable organization.
Mayo came up big in the second half for USC. He scored 20 points after the break and made five 3-pointers total, including a long shot that sparked a 9-0 run at the start of overtime to put the Trojans up 83-74 with three minutes left.
This time, Oregon couldn't rally, getting no closer than 85-82 before Hackett drained the Trojans' 12th 3-pointer of the game. USC ended on a 10-4 run.
The Trojans led 66-57 with 1:26 to play when Porter went to the line, where three free throws started a 17-8 run. Hairston scored seven points during that stretch, and Porter had six.
Hackett had a chance to make it a three-point game but missed one of his two free-attempts with 14.6 seconds remaining.
Porter drove the lane at the other end but missed the tying layup. Oregon regained possession under the basket with 2 seconds left, and Kamyron Brown found Taylor cutting to the hoop for the uncontested layup as time expired.
Neither team shot the ball well in the first half, particularly from the 3-point line. Southern Cal was 2-for-12 from long range, while the Ducks converted just three of their 14 attempts.
The Trojans could never pull away despite leading the entire half, while Oregon could never get closer than five points after falling behind 14-5 early on.
But the Trojans shot 77 percent in the second half and were perfect in overtime. They made 12-of-26 overall from the 3-point line.