SEATTLE -- Not even J.A. Happ himself saw a 20-win season coming at this point in his career. And the 33-year-old Toronto Blue Jays starter certainly didn't see No. 20 coming as easily as it did Tuesday night.

Happ had to throw just five innings -- not including the warmup tosses he made inside the visiting clubhouse during a top-of-the-fourth-inning that lasted nearly 40 minutes -- to become baseball's second 20-game winner as the Blue Jays used an eight-run fourth to blow out the Seattle Mariners 10-2 on Tuesday night.

"You don't get to that number without having great teammates," said Happ, who improved to 20-4 after never previously winning more than 12 games in a season. "I'm really grateful just to be on this team."

Happ pitched five innings, allowing two runs off six hits, and he didn't need his A-game on a night when Toronto piled up 14 hits, including four home runs.

"We've been looking for that outbreak," said right fielder Michael Saunders, whose two-run homer broke a 2-2 tie in the eight-run fourth. "We know we have the guys in the locker room who have the capability to do it."

The Blue Jays (83-68) moved into sole possession of the top spot in the American League wild-card standings, one game ahead of Baltimore. Seattle (79-72) is three games behind the Orioles in the race for the second and final spot.

Saunders, Russell Martin, Josh Donaldson and Edwin Encarnacion each hit a home run for the Blue Jays, while teammate Kevin Pillar added three hits. Jose Bautista, Troy Tulowitzki and Ezekiel Carrera had two hits apiece. All nine players in the Blue Jays' starting lineup scored.

Encarnacion hit his 42nd home run of the season -- two behind American League leader Mark Trumbo while matching Encarnacion's career high -- and drove in three runs.

Robinson Cano went 2-for-4 and drove in the only two runs for the Mariners, who had seven hits in the loss and have now scored two runs or fewer in five of their past six games.

The Blue Jays scored eight runs in the fourth inning -- a frame that took nearly 40 minutes to complete, highlighted by towering two-run home runs from Martin and Saunders as they rallied from a 2-0 deficit.

Saunders, a former Mariner, broke a 2-2 tie with his 24th home run of the season, a 385-foot shot to right. Carrera added an RBI single two batters later and came around from first base to score on Devon Travis's pop-up single near the right-field line.

Encarnacion, who started the inning with a strikeout before nine consecutive batters reached base, added an RBI double in a frame that saw the Blue Jays pile up eight hits and a walk sandwiched between the first and second outs.

"It got away from us there," Seattle manager Scott Servais said.

Martin's two-run homer tied the score 2-2 after Cano drove in two runs in the third with a strange, seeing-eye triple.

With two outs and runners on second and third, Cano hit a sharp grounder to the left of Toronto second baseman Travis, who slid to make a play on the ball -- only to have it bounce off his knee and fly all the way into the right-field corner.

Six consecutive Toronto hitters recorded hits to chase Seattle starter Hisashi Iwakuma in the fourth. Iwakuma allowed six runs (five earned) and eight hits over 3 1/3 innings. Mariners catcher Chris Iannetta misplayed a routine pop fly in foul territory, allowing Bautista to extend his at-bat and start the onslaught with a single.

"That's kind of been the story of our season," Servais said. "We're really, really good, or we have some ugly nights."

NOTES: Mariners slugger Nelson Cruz served as the designated hitter again Tuesday, the 29th consecutive game in which he was Seattle's DH. Cruz was the Mariners' Opening Day right fielder and was supposed to split time between the positions, but settled in as an everyday DH over the past five weeks. ... The Blue Jays and Mariners wrap up the three-game series Wednesday afternoon, when Toronto RHP Aaron Sanchez (13-2, 3.17 ERA) opposes Seattle RHP Felix Hernandez (11-6, 3.79 ERA). Both teams have Thursday off before Seattle opens a three-game series in Minnesota and the Blue Jays begin a four-game home series with the New York Yankees on Friday.