ST. PETERSBURG -- The Mariners arrived at Tropicana Field on Saturday knowing that they faced a tall task by deploying a bullpen game against a Rays club directly ahead of them in the American League Wild Card standings.

And even with a gritty effort from opener Trent Thornton, bulk-innings pitcher Luke Weaver and the other three arms that manager Scott Servais deployed, by the time the dust settled, Seattle was outlasted by Tampa Bay in a 7-5 walk-off loss, its ninth this season. The defeat, coupled with Toronto’s win, moved the Mariners and Blue Jays into a tie for the second AL Wild Card spot.

• Games remaining: at TB (1), vs. LAA (3), vs. LAD (3), at OAK (3), at TEX (3), vs. HOU (3), vs. TEX (4)
• Standings update: The Mariners (79-63) are 1 1/2 games behind the Astros (81-62) for the AL West lead, with the Rangers (77-64) 1 1/2 games behind Seattle. The Mariners are tied for the second AL Wild Card spot with the Blue Jays (79-63). The Mariners also fell to 7 1/2 games back of the Rays (87-56) for the top Wild Card spot.

Tayler Saucedo entered in the ninth and surrendered a two-out walk to No. 9 hitter Taylor Walls, then a walk-off two-run homer to All-Star Yandy Díaz, who just narrowly cleared the right-field wall with a Statcast-projected 364-foot shot. Saucedo’s pitch was a changeup on the outside corner in a 1-2 count.

The walk that preceded it proved more costly, as Saucedo needed just four pitches to record his first two outs before walking Walls on a full count.

“Sauce threw the ball really well, he did,” Servais said. “He's been fighting a finger issue. He's been down a couple of days. I thought he threw the ball really good.”

The Mariners led most of the afternoon, beginning with a three-spot in the first inning against Aaron Civale, who couldn’t find the strike zone. Seattle nearly made it a six-run lead, but Josh Rojas’ 342-foot line drive just barely hooked outside the right-field foul pole, then he flied out to left. 

That was the first of two close calls, the other being a ground-rule double from Brian O’Keefe in the seventh that was initially ruled his first career homer. However, an umpire review ruled that the ball had caromed off the top of the left-field wall. In the next at-bat, O’Keefe was doubled off to end the inning after J.P. Crawford ripped a line drive directly at the second baseman. 

“That home run would have been huge for us to extend our lead a little bit,” O’Keefe said. “But they came back, and they continued to press us.”

The Rays pulled into striking distance in the fifth, when Weaver surrendered a two-run double to Brandon Lowe after a one-out single and a walk. Weaver then gave up the tying run in the seventh via a ground-rule double and a bloop single, after which Gabe Speier surrendered a go-ahead knock to Díaz, who entered as a pinch-hitter. 

Speier nearly struck out Díaz on a sinker up and in and was frustrated about it after he got out of the inning. Eugenio Suárez then scored on a wild pitch in the eighth to retie the game at 5.

The Mariners’ bullpen game strategy manifested on Friday after it was determined that Bryan Woo needed a few extra days’ rest. The rookie is at 114 innings this season (including nine Minor League starts), well beyond the 57 he threw last year, when he made his pro debut after recovering from Tommy John surgery. Woo is slated to start Tuesday against the Angels.

The positive on Saturday was that the Mariners nearly eked out a win against a likely playoff-bound team when their pitching situation was hamstrung. The negative was obviously that they couldn’t clear the finish line and weren’t able to make up ground on Houston in a historically close AL West race.

If the playoffs began today, the Mariners would visit the Rays at The Trop in a best-of-three AL Wild Card Series beginning on Oct. 3. And if this back-and-forth weekend is a preview, it could be a tense series.

Seattle would prefer to avoid that scenario, which would include cross-country travel on the heels of a 10-game gauntlet to finish the regular season, with three at Texas, three at home against Houston then four against Texas -- a stretch that will likely determine the division. 

“We're playing one of the best teams in baseball,” Ty France said. “So every single game, it matters, and unfortunately, we haven't been able to come out on top last two nights.”

Winning the AL West would mean avoiding the AL Wild Card Series altogether -- assuming Minnesota remains the lowest division-winning seed in an underachieving AL Central -- with a first-round bye.

The Mariners’ first division title since 2001 is within reach, but with 19 games to go, the stakes are growing more paramount with each passing day -- and losses such as Saturday’s loom a little larger.