BERKELEY – USC hasn't been a big home run-hitting team this season, but the Trojans hurt Cal with the long ball Friday night.

A homer from CJ Stubbs tied it in the sixth inning and a two-run shot by Jamal O'Guinn untied it in the eighth as the Bears suffered a 9-4 loss at home in the Pac-12 baseball opener for both teams.

Cal did plenty of long-distance damage too, with Sam Wezniak and Korey Lee both homering in the bottom of the third to put the Bears on top 4-3. But the Bears didn't play nearly well enough defensively in the opener of this three-game series.

Three errors, all committed in the third inning, led to a three-run USC rally that put the Bears (8-7, 0-1 Pac-12) in an early hole. And there's no doubt that playing sounder defense will be an emphasis when the teams continue this series Saturday afternoon.

Sam Stoutenborough took the loss on the mound for Cal, but the freshman once again was stellar in a long-relief role. He took the mound to start the fourth and held the Trojans (6-10, 1-0) to two hits over 4 1/3 innings, striking out five and walking one. He did give up the tying homer to Stubbs, but Stoutenborough already is emerging as a foundation piece for the Bears' young pitching staff.

Arman Sabouri, settling in as the Friday "opener" for Cal, went 2 1/3 innings and was charged with the three third-inning runs, none of them earned. O'Guinn's homer in the eighth, which broke a 4-4 tie, came off Sean Sullivan. But the Trojans entered the game with just six home runs in their first 15 games.

Lee's homer, a three-run blast to the opposite field in right, was his second in as many games. Andrew Vaughn went 3-for-4 with a run, but the Bears totaled just eight hits as a team.

The second game of the series is slated for 3:05 p.m. Saturday.