Atlee Hammaker pitched a three-hitter for his second straight shutout and Chili Davis drove in three runs with a homer and a sacrifice fly yesterday to lead the San Francisco Giants to a 5-0 victory over the Cubs in Chicago.

"I was fortunate," said Hammaker, a 25-year-old left-hander from Mount Vernon High School in Alexandria. "I didn't have a good breaking ball and my fast ball left me at the end. I was lucky to get the shutout, but I'll take one any time I can get it."

Hammaker (2-1) had a tough act--his own--to follow. In his last start, he pitched seven perfect innings against Cincinnati and finished with a two-hitter. At Wrigley Field yesterday, he did not allow a hit for five innings until the Cubs' Larry Bowa led off the sixth with a bloop single to center.

"I've always had good control," said Hammaker, who didn't know how much he was helped by a 23-mph wind blowing in. "Maybe it held up some extra base hits, but who knows?"

"They got him five runs early and with the wind blowing in all he did was throw fast balls and challenge the hitters," said Cubs Manager Lee Elia. "He has uncanny control for a left-hander."

Hammaker gave up a two-out single to Ron Cey in the seventh and then issued his first walk this season after 21 2/3 innings to Leon Durham before ending the inning by retiring Keith Moreland on a fly to right. Ryne Sandberg singled in the ninth for Chicago's other hit.