PULLMAN, Wash. — Oregon's Spencer Steer hit a ninth-inning grand slam to force extra innings Sunday, but Washington State got the walk-off win on a passed ball in the 10th to avoid a series sweep as the Cougars beat the Ducks 8-7 in Pac-12 baseball.

With two out in the 10th, Washington State's Collin Montez reached on an infield single and took second on a throwing error. Montez took third on a wild pitch, and scored game-winner when Oregon reliever Ryne Nelson walked Brody Barnum on a high-and-tight pitch that popped out of the glove of catcher Cameron Campbell.

The victory was the first of the Pac-12 season for the Cougars and also ended a five-game winning streak for Oregon.

Steer's grand slam was his second home run of the day. His first got Oregon (21-13, 7-5 Pac-12) on the board in the fourth inning, after WSU (8-25, 1-11) had jumped out to a 3-0 lead.

The Cougars led 7-3 in the ninth inning but the Ducks loaded the bases with a pair of walks and infield single. With two outs, Steer hit his second grand slam of the weekend to tie the score. He finished the three-game series 7-for-14 with 11 RBIs.