Pitcher Randy St. Claire got a bunt single in his first major league at bat to open Montreal's two-run rally in the 15th inning as the Expos defeated the Giants, 4-2, yesterday in San Francisco.

St. Claire, a right-hander and the Expos' fourth pitcher of the game, earned his first major league decision by allowing two hits and no runs in four innings.

"The hit I don't really care about," St. Claire said. "Getting that first win is great.

"I bunted on my own. I figured my chances of getting a hit any other way weren't very good."

The rookie came into the game after Jeff Reardon, the Expos' relief ace, worked three scoreless innings. St. Claire batted for himself in the 15th because Montreal had exhausted its supply of rested relievers.

The leadoff bunt was the Expos' only hit in the 15th. Both runs off Frank Williams (0-2), the fourth Giants pitcher, were unearned.

Third baseman Chris Brown fielded the bunt and made a throwing error to first, allowing St. Claire to reach second. An infield out advanced St. Claire, and U.L. Washington was walked intentionally.

Vance Law topped a slow grounder that Williams fielded. He threw low to the plate for an error as St. Claire scored, knocking down catcher Bob Brenly. The ball rolled to the backstop and Washington scored.