George Bell hit a two-run homer and Dave Stieb held Detroit to three hits last night as the Toronto Blue Jays beat the Tigers, 2-0, in the first game of their important weekend series.

The victory, before 48,002 fans at Tiger Stadium, gave the American League East-leading Blue Jays a 3 1/2-game lead over second-place Detroit. Stieb (8-5) struck out six and walked two.

Dan Petry (9-6), who has won only once since May 22, pitched a five-hitter. He has pitched 21 straight innings without benefit of a run.

"No, I don't appreciate it," he said when asked if he could appreciate the artistry of Stieb's performance. "Too many good games are being pitched against me for me to admire what they're doing. I'm trying to win games.

"He didn't have to do that tonight. He could have pitched another good game and lost, 3-2. I'd rather have people feel sorry for him than sorry for me."

Willie Upshaw hit a leadoff single in the Toronto second and scored on Bell's 14th homer of the season, a shot into the upper deck in right.