Colorado receiver Shay Fields caught three touchdown passes, the defense kept Oregon State out of the end zone and the Buffaloes posted their biggest Pac-12 victory with a 47-6 win Saturday in Boulder, Colo.

The Buffaloes (4-1 overall, 2-0 Pac-12) are off to their best start since joining the league in 2011. They had a total of five conference victories in their first five seasons. Colorado hasn't been 4-1 since 2005, which was Gary Barnett's final season as head coach.

Fields scored all of his touchdowns in the first 19 minutes of the game. He scored from 51, 33 and 63 yards, the last coming when he turned a quick pass into a sideline dash, sprung by a block from receiver Devin Ross for a 21-3 lead.

Fields caught seven passes for a career-high 169 receiving yards.

Oregon State (1-3, 0-1) made a quarterback switch from Darell Garretson (5 of 16 for 55 yards) to walk-on freshman Conor Blount in the second quarter, but it didn't help. Blount completed 8 of 16 passes for 50 yards with two interceptions.

Colorado linebacker Rick Gamboa returned his pick 20 yards for a touchdown in the final minute of the first half to give the Buffaloes a 37-6 halftime advantage.

Colorado quarterback Steven Montez, making his second start in place of injured Sefo Liufau, completed 19 of 27 passes for 293 yards and all three touchdowns to Fields. Running back Phillip Lindsay led the charge on the ground with 16 carries for 90 yards and a touchdown.

Oregon State's only points came on first-half field goals of 32 and 40 yards from Garrett Owens.

Colorado, which sustained its lone loss at Michigan (where Liufau was injured when the Buffs had a 28-24 lead), is trying for its first bowl appearance since 2007. Liufau could be available next week at USC.

The Buffaloes' previous biggest Pac-12 victory was 48-29 over Arizona in 2011.