SANTA CLARA, Calif. >> Marcus Mariota threw for 303 yards and two touchdowns and ran for a career-high three scores, and No. 3 Oregon likely secured a playoff spot by overwhelming eighth-ranked Arizona 51-13 in the Pac-12 championship game Friday night.

On a rainy night in Silicon Valley, Oregon wiped out the Wildcats in front of a sparse but rowdy pro-Ducks crowd — announced as 45,618 — that sprinkled the red seats at $1.3 billion Levi’s Stadium bright yellow and green.

Mariota — the Saint Louis School product — also boosted his credentials for the Heisman Trophy as the Ducks turned the patchy field into their personal playground.

Oregon outgained Arizona 640 to 224 yards. The Ducks ran for 324 yards and held the Wildcats to 111 on the ground.

“This is a huge accomplishment for us,” Mariota said. “Now we need to continue to improve and get better for whoever comes next.”

The victory avenged Oregon’s only loss this season — a 31-24 setback to Arizona on Oct. 2 in Eugene — and a 42-16 loss in Tucson last year that kept the Ducks out of the conference championship game.

The selection committee will announce the four-team playoff field Sunday, and Oregon is almost surely guaranteed a berth. The Ducks (12-1) entered the week ranked second in the playoff standings.

Mariota was inconsistent at the start, leading Oregon to field goals and a 6-0 first-period lead despite dominating field position and the game.

He broke through with a 7-yard touchdown run with 7:27 left in the half for a 13-0 lead. His 4-yard run with 1:34 left made it 20-0 and capped a six-play, 79-yard drive. The Ducks got a field goal to end the half for a 23-0 lead.

Looking more comfortable in the second half, Mariota’s first touchdown pass came in the third period when he hit track star Devon Allen on a 4-yard score to make it 30-0. Mariota has thrown a touchdown pass in every college game — 39 — he’s played in his three-year career for Oregon.

Mariota passed 11 yards to Darren Carrington for another score and a 37-7 lead. He capped his day with a 1-yard run with 4:54 left in the third period for a 44-7 lead.

Mariota completed 25 of 38 passes and rushed 10 times for 33 yards.