Dickey (9-11) went 7 2-3 innings, allowing one run on eight hits. The knuckleballer struck out five and walked two to earn his first win since July 1. Casey Janssen worked the ninth for his 20th save in 22 opportunities.
Hisashi Iwakuma (10-5), who pitched 7 1-3 innings, took the loss. He allowed two runs on four hits, striking out two and walked a season-high three.
Justin Smoak hit his 11th home run in the seventh to give the Mariners a 1-0 lead at the time. Since July 1, Smoak is batting .327 with 16 runs, eight doubles, five homers and 13 RBI. After Smoak's home run, the Jays responded with their three-run eighth-inning rally. Brett Lawrie opened with a triple into the right-center gap.
With one out, Jose Reyes lined a RBI single to center, ending Iwakuma's outing.
Yoervis Medina then complicated the situation for the Mariners, giving up a single to Jose Bautista. Both runners advanced on Medina's wild pitch. Edward Encarnacion walked to load the bases.
Oliver Perez entered as did DeRosa, who lined his go-ahead single to left on an 0-2 pitch. DeRosa is 5-of-14 as a pinch hitter this season with six RBI.
The Mariners put together a rally in the third. Humberto Quintero opened with a ground-rule double that bounced over the left-field wall. With one out, Kyle Seager singled to right, with Quintero holding at third.
Kendrys Morales then hit a two-hopper to third baseman Lowrie, who dived to his left to stop it. From his knees, he started a 5-4-3 double play to end the threat.
The Blue Jays walked into a Iwakuma-induced rally in the fourth. With two outs, Iwakuma issued a base on balls to Bautista. Iwakuma is third in the league with the fewest walks per inning at 1.44.
He then walked Encarnacion, the first time he has walked two batters in an inning this season. He then induced Adam Lind to bounce out to second.
The Mariners have had 51 of their 112 games decided by two runs over fewer.
NOTES: Dustin Ackley started at his old position, second base. He had been the team's regular at that spot but a batting slump and Nick Franklin's emergence pushed him to the outfield. "They always told me to be ready, just in case. I see why now," Ackley said. Acting manager Robby Thompson said, "I don't hesitate for a minute to put him out there." . manager Eric Wedge, who suffered a mild stroke July 22 and has missed 13 games, will miss more. There was hope that he could rejoin the team by this homestand but as Thompson said, "he's doing well. It is a slow process...when that time is, we're not really sure." . LHP J.A. Happ was added to the Blue Jays' roster before the game, replacing RHP Steve Delabar (shoulder), who was placed on the 15-day DL. RHP David Schwimer was designated for assignment to make room for Happ on the 40-man.