Joe Ferguson slugged a three-run homer and doubled twice to lead Los Angeles to a 9-2 vitory over San Francisco yesterday as the Dodgers opened a three-game lead over the Giants in the National League West.

Doug Rau (13-8) and Rick Rhoden combined to scatter, seven hits as Los Angeles swept the two-game series.

Ron Cey belted his 18th homer off loser Jim Barr, who has dropped seven straight decisions to the Dodgers. The Giant's right-hander has not defeated Los Angeles since September 1974.

After Heity Cruz hit his seventh homer of the year in the top of the second, the Dodgers jumped on Barr for three runs in the bottom half, two on Cey's homer.

Rick Monday's base-loaded single produced two more runs in the third and then Ferguson hit a three-run homer in the fifth, his 13th of the year.

Ferguson doubled to score Monday in the seventh for his fourth RBI.

Darrell Evans hit his 17th homer in the fifth of the Giant's other run.

Los Angeles, matching its biggest lead of the season, has won seven of its last nine games and 22 of its last 30.

After Rau singled home the Dodgers' third run in the second inning, Dave Lopes walked to fill the bases with one out. But a base-running error prevented the Dodgers from adding to their lead. Bill Russell lined sharply to Jack Clark in right field, and Clark was able to double Rau off second.

An inning later, following Monday's two-run single, Ferguson was walked intentionally to fill the bases with one out. Barr got out of the jam when Rau grounded into a double play.

Rhoden relieved Rau at the start of the eighth and gave up singles to Herndon and Hill. LeMaster and pinch hitter Terry Whitfield struck out before Madlock walked to load the bases. But Evans popped out to run the Giants' left-on-base total to 12.