The Orioles (76-59) entered the game in second place in the American League East, one game behind the New York Yankees. The Blue Jays (60-75) were fifth, one game behind the Boston Red Sox.
The victory was the Orioles' 21st in their past 29 games. The Blue Jays are 9-25 since July 30. The Blue Jays were outhit 18-4.
Britton (5-1), who led the Orioles with 11 wins last season, was making his ninth major-league start this year after opening the season on the disabled list with a shoulder impingement. He made 11 starts in the minors.
He struck out eight while walking two, one of which was intentional, in winning his fourth start in a row. Toronto starter Carlos Villanueva (7-5) allowed seven hits and was charged with six runs in 6 2-3 innings as the Blue Jays lost their fourth game in a row.
The game was 0-0 through four innings and Adam Jones opened the fifth with a double into the right-field corner. Matt Wieters flied out to right and Jones tagged at second. Shortstop Yunel Escobar jumped to cut off the throw from Moises Sierra but neglected to make the tag as Jones got back.
Chris Davis walked. Reynolds hit his 17th homer of the season to left field to put the Orioles into a 3-0 lead.
The Orioles scored again in the sixth inning as rain began to fall with the Rogers Centre roof open.
Nick Markakis led off with a single, took third on a double by J.J. Hardy and scored on a sacrifice fly to centre by Nate McLouth.
Davis opened the seventh with a single, moved to third on a double by Manny Machado and came home on Robert Andino's sacrifice fly to left.
Left-hander Aaron Loup replaced Villanueva and immediately balked in the sixth run of the game.
Markakis doubled and scored on a single by Hardy.
Jones and Wieters led off the five-run eighth with singles and Davis knocked in one run with a double. Chad Beck replaced Loup and gave up run-scoring singles to Reynolds and Machado.
Markakis doubled with one out to score a run. Hardy reached first on Beck's error and McLouth singled in a run.
Notes: Some of the announced crowd of 13,556 at Rogers Centre used umbrellas or scurried to cover as technical difficulties with the roof in the sixth inning meant the roof closed more slowly than usual ... Outfielder Anthony Gose and right-handed reliever Beck joined the Blue Jays Tuesday as call-ups from triple-A Las Vegas. ...Catcher J.P. Arencibia (fractured right hand) was 0-for-4 with a walk playing while behind the plate for Dunedin in the single-A team's 1-0 playoff loss to Lakeland on Tuesday on his rehabilitation assignment. ...Brandon Morrow (8-5, 2.93 earned-run average) will start Wednesday's series finale for the Blue Jays against Miguel Gonzalez (6-3, 3.31 ERA).