The Beavers (7-6) stopped a five-game slide and set several records in handing Boise State its worst loss in two months.
Biletnikoff Award-winner Brandin Cooks had 60 yards receiving and a touchdown while setting a Pac-12 record for most receiving yards in season, passing Southern California's Marqise Lee. Sean Mannion set another for passing yards, finishing 24 of 33 for 259 yards and a touchdown.
Oregon State kept Boise State out of the end zone until the third quarter, well after the Beavers had opened a big lead.
Reynolds had his first fumble recovery about 12 minutes into the game when Scott Crichton stripped Boise State quarterback Grant Hedricks in the end zone. The ball popped forward to the 3-yard line, where Reynolds picked it up and ran it in.
Reynolds tacked on another fumble return in the second quarter on his way to game MVP honors. Troy Ware caught a 6-yard pass near the sideline for Boise State, but Larry Scott punched the ball out as Ware was falling to the ground. Reynolds picked it up and ran 70 yards to the end zone.
Matt Miller led Boise State with 11 catches for 206 yards and a touchdown, with most of the production coming after the game was decided. Miller, who set a school season record with 88 catches, was the Broncos' MVP for the game.
Boise State's most successful drive came in the third quarter after Oregon State went 94 yards and scored a touchdown to make it 38-6. The Broncos responded with a nine-play, 76-yard drive spent partially in a hurry-up offense. Jay Ajayi took a shotgun handoff from Hedrick and ran up the middle for a 1-yard TD.
After the successful extra-point attempt went into the stands, the mostly-empty stadium provided its loudest ovation of the night in support of the fans who tried to keep the ball away from security by throwing it around the seats.
Oregon State finished with 454 total yards, averaging 6.8 per play.
Hedrick threw for 382 yards and a touchdown, closing out a difficult stretch for the Broncos (8-5).
Joe Southwick was sent home by interim coach Bob Gregory after the quarterback was accused of urinating off a hotel balcony in Honolulu last week, though he later told a TV station he didn't do it and was unfairly dismissed.
It was Gregory's first major issue after taking over for Chris Pedersen, who left the team to take over at Washington.
Both teams started the game with similar drives, making progress on big plays before stalling in the red zone and kicking field goals. But Oregon State grabbed the lead for good on Cooks' 2-yard TD reception with 4:15 left in the first quarter, capping a 92-yard drive.