The Mariners have used their starting pitching to move ahead and can push Toronto further back if Hisashi Iwakuma continues to pitch like he has since the start of July.
Iwakuma has also pitched well against the Blue Jays as he looks to help Seattle complete a nine-game homestand with a sweep Wednesday night.
The starters employed by Seattle (64-55) in this series have yielded one run in each contest. Felix Hernandez gave up three hits in seven innings of Monday's 11-1 rout and Chris Young allowed two in Tuesday's 6-3 victory.
Mariners starters own an AL-best 3.27 ERA.
"Top to bottom the (Seattle) pitching staff - rotation and bullpen - is one of the best in baseball,'' Toronto manager John Gibbons said. ''But we have got to score for our staff.''
Seattle has moved into a tie with plummeting Detroit for the AL's second wild card, with Toronto (63-58) falling two games back.
''It's awesome. It's a whole new ballgame when it means something and you get in here and you're pumped and you look and see what everyone else is doing and where you stand,'' said left fielder Dustin Ackley, who has four RBIs in this series. ''It's a lot more fun. Baseball is always fun but it makes it that much more enjoyable when you're actually in it.''
The Mariners will like their chances of a sweep that would complete an 8-1 homestand if Iwakuma (10-6, 2.86 ERA) maintains the mound mastery that has seen him go 5-2 with a 2.04 ERA in eight outings since the start of July. He has lasted at least seven innings in seven straight, and owns a 1.66 ERA in the last three.
The right-hander, who limited the White Sox to a run over seven innings in Friday's 4-1 win, is 2-1 with a 1.61 ERA in three career starts against the Blue Jays. He has held Colby Rasmus hitless in 11 at-bats, and Dioner Navarro is the only available Blue Jays hitter who has homered off Iwakuma.
Toronto starter R.A. Dickey (9-11, 3.99) hopes to avoid matching San Diego's Eric Stults for the major league lead in road losses. Dickey is 3-8 with a 3.79 ERA in 12 such outings.
The knuckleballer yielded two runs over six innings Friday and was in line for a victory before the bullpen blew a two-run lead in the ninth inning of a 5-4 home loss to the Tigers.
Dickey showed how unpredictable his results can be in two starts against Seattle last year, giving up seven runs over six innings in an 8-1 defeat May 4 before allowing one run in 7 2-3 innings to earn a 3-1 road win Aug. 5.
He is most familiar with Robinson Cano, who is 6 for 23 against him and third in the majors with a .330 average. Logan Morrison is 5 for 17 off Dickey.
Morrison is 15 for 45 during a 13-game hitting streak, going 3 for 6 in this series.
Blue Jays slugger Adam Lind went 0 for 3 on Tuesday in his first action since July 7 after missing 28 games with a right foot injury. The club will play one final time before Edwin Encarnacion is expected to be activated Friday.