Thorpe, making his first career game-one series start, allowed just one hit out of the infield. California's first hit came on a bunt in the first inning and the third hit was a high chopper to third base in the seventh inning.
The Ducks' lefthander struck out seven in 7.1 innings, while allowing two runs (one earned). Jimmie Sherfy pitched a perfect ninth inning to pick up his 10th save.
The Ducks took the early lead with a run in the top of the first inning. Mitchell Tolman singled to right center field driving in Thomas for a 1-0 lead. Oregon tried to add a run but Tolman was thrown out trying to score on a double by Scott Heineman to end the inning.
Oregon took the lead in the top of the fifth with a pair of runs. Altobelli drove in Josh Graham with a base hit to right field to put the Ducks up 2-1. Altobelli made it 3-1 scoring on a sacrifice fly by Aaron Payne.
The Bears cut the lead to 3-2 in the bottom of the sixth when Mike Reuvekamp scored on a wild pitch by Thorpe (10-3).
Game two between Oregon and Cal is at 6 p.m. Saturday night.