The Golden Bears (8-4-0, 1-1-0) opened the scoring in the eighth minute on a penalty goal by Kaitlyn Fitzpatrick. Cal then added a second score by Celeste Boureille in the 36th minute.
"It was a disappointing start to fall down a goal within the first seven minutes," said Oregon head coach Tara Erickson. "We regrouped really well at halftime and came out much stronger in the second half. We were better able control our touches therefore we finished the game off strong."
The loss dropped the Ducks to 0-1-1 in Pac-12 play and 5-4-2 overall.
Cal outshot the Ducks 11-8, including an 8-5 edge in the first half when Cal scored all of its goals.
Bri Pugh led the Ducks with three shot attempts. Oregon also had a pair of shots from Scout Libke, while Kristen Parr, Achijah Berry and Maryn Beutler each had one.
The Ducks return to action Sunday to face defending NCAA champion and second-ranked Stanford.
"Cal dominated most of the first half, as was evident with the score at halftime, but we calmed down and played our style of soccer in the second half," said Erickson. "We look to learn from this game, regroup and bounce back against Stanford on Sunday."