Jay Johnstone hit a three-run homer in the fourth inning and Ferguson Jenkins pitched a seven-hitter to lead the Chicago Cubs to a 5-3 victory over the St. Louis Cardinals yesterday in Chicago.

The victory was Chicago's first against St. Louis this season after six losses.

Johnstone's homer, his fifth since being acquired by Chicago three weeks ago, came off Joaquin Andujar (6-5). Bill Buckner led off the fourth with a single and Leon Durham walked. Johnstone then homered to right field to give the Cubs a 3-0 lead.

Johnstone was released by the Los Angeles Dodgers late in May, and, although several other clubs offered him a job, he decided to join the Cubs where he would get a chance to play.

"I came here because I knew I'd get the opportunity," said Johnstone who had been used strictly as a pinch hitter for the last year and a half.

"I told them I could play and they said, 'Here's the glove, show us,' " said Johnstone, who has driven in 15 runs and batted .300 with the Cubs.

"I could have gone to Pittsburgh, Philadelphia, San Diego or Cincinnati," said Johnstone, "but I would have been a pinch hitter there. Here I get to play."

Jenkins (5-8) struck out four and walked two in pitching his second complete game of the season and only the third for the Cubs' staff.

The Cardinals scored in the sixth when Lonnie Smith led off with a single, stole second, went to third on Willie McGee's infield out and scored on a sacrifice fly by Keith Hernandez.

The Cubs' Larry Bowa had three singles for his fourth straight three-hit game.