PORTLAND, Ore. - John Adamson’s walk-off single to deep right-center brought Caleb Tommasini across the plate and propelled Oregon to a 3-2 victory over Oregon State in front of a Pac-10 record crowd of 15,540 fans at PGE Park on Saturday night.

“I was just trying to be aggressive like Coach Horton told me to,” Adamson said after his game-winning pinch hit in the bottom of the 10th. (Sam Gaviglio) was throwing a lot of fastballs, so I was sitting on the fastball and he threw one to me on the first pitch. When the ball went over the right fielder’s head, the feeling was indescribable.”

The win also had two significant meanings. It was the 500th career Division I victory of George Horton’s career and it also marked Oregon’s (11-13, 1-1) first Pac-10 win this season.

“The 500th win is just a little asterisk on the great victory,” Horton said. “This was a tremendous atmosphere and with the crowd as large as it was it felt like Omaha.”

Oregon right-hander Drew Gagnier earned his first win of the season after pitching the final two innings of the game and holding Oregon State scoreless. The sophomore struck out the side in order in the top of the 10th to set up Adamson’s game winner.

Oregon senior Caleb Tommasini was walked to lead off the 10th and sophomore Mitch Karraker executed a sacrifice bunt down the first baseline to move the speedy center fielder into scoring position before Adamson was called to the plate to pinch hit.

The Ducks erased Oregon State’s two-run lead in the bottom of the eighth when freshman KC Serna was at the plate and had the bases loaded with two outs against him. OSU lifted reliever Kraig Sitton in favor of left-hander Josh Osich to face the Ducks’ starting shortstop. On a full count, Osich delivered ball four to walk in Danny Pulfer for the Ducks first run of the game. Darrell Hunter was then called into pinch hit for Oregon, and the freshman patiently waited out Osich as the lefty delivered four straight balls and walked in Tommasini for the game-tying run.

OSU’s John Wallace squashed six innings of scoreless baseball when he delivered a two-out RBI single to center field off Oregon starter Erik Stavert, bringing Stefen Romero across the plate from second for the game’s first run.

After pitching 6 and 2/3 innings, Stavert was relieved by junior lefty Ryan Fleckenstein. The Livermore, Calif., native held the Beavers to one run on five hits in his sixth start of the year. With two runners on, Fleckenstein struck out Joey Wong to end the seventh for OSU.

Right-hander Madison Boer started on the mound for Oregon in the eighth, and the Beavers tapped the freshman for their second run with Romero’s one-run double to deep right center, scoring Ryan Ortiz all the way from first.

Oregon and Oregon State will play the rubber game of their series at 1 p.m. tomorrow at PGE Park. The game is scheduled to air on Comcast SportsNet.

Notes: Saturday’s game was delayed one hour because of rain showers...Oregon head coach George Horton returned to the dugout after serving his three-game suspension...Eddy Rodriguez pinch hit in the bottom of the seventh...it was his first return to action since spraining his right knee at Nevada on March 14.