Mark Bomback retired the first 16 Oriole batters today and Willie Upshaw hit a home run in the eighth inning to snap a 2-2 tie as the Toronto Blue Jays salvaged the last game of a four-game series with a 4-2 victory at Memorial Stadium.

Thus ended a four-game Baltimore winning streak and a run of 19 Blue Jay losses at Memorial Stadium since July 1978.

Upshaw led off the eighth with his second home run of the season, over the 376-foot mark in right field on a 2-2 pitch from Steve Stone (1-3), the 1980 Cy Young Award winner. There was little doubt about the distance from the crack of the bat, although Ken Singleton tried to climb the wall.

Bomback and Stone each had a shutout through five innings. The Toronto right-hander, 10-8 with the New York Mets in 1980, was traded in a surprise move to Toronto April 6 for a minor-league pitcher. He threatened from the start today to add his name to the list of fine pitchers the Mets have let get away.

Relying heavily on a changeup most of the 23,898 fans would have jumped at a chance to swing at, Bomback improved his record to 3-1 by inducing 14 of 22 outs on ground balls before his arm stiffened in the eighth. He was perfect until one out in the sixth, when Gary Roenicke caught a hanging curve and stroked a line double to the left field corner.

One out later, Al Bumbry drove a 3-2 delivery 340 feet and over the right field wall for a two-run homer.

Otherwise, "I got the ground balls I needed and that's the way I like to pitch," said Bomback.

Toronto broke open the scoreless tie in the sixth on singles by Upshaw and John Mayberry and a sacrifice fly by Al Woods. After Bumbry gave the O's the lead, the Jays made it 2-2 in the seventh, Garth long singling and eventually scoring when a Stone pitch broke off Dan Graham's mitt for a passed ball.

They tacked on an insurance run in the eighth after Upshaw's homer.