ST. PETERSBURG -- In a venue and against an opponent that could very well represent the Mariners’ first matchup of the postseason, Seattle began this crucial four-game series with an imposing start on Thursday night, holding on for a 1-0 win over the Rays at Tropicana Field in an outcome that wasn’t decided until the last pitch.

On the mound for the third day in a row for the first time in his career, Andrés Muñoz hit his leadoff batter, issued a one-out walk, then saw that runner reach scoring position with a stolen base to put Seattle’s longstanding but slim lead in peril.

But after a quick consultation with catcher Cal Raleigh, who’d just recorded his second caught stealing of the night, and pitching coach Pete Woodworth, Muñoz struck out pinch-hitter Harold Ramírez on his slider, the topsy-turvy pitch that’s vital to his arsenal.

Muñoz completed Seattle’s 14th shutout of the year and just the sixth for Tampa Bay’s offense, the club directly ahead of the Mariners in the American League Wild Card standings.

• Games remaining: at TB (3), vs. LAA (3), vs. LAD (3), at OAK (3), at TEX (3), vs. HOU (3), vs. TEX (4)
• Standings update: The Mariners (79-61) remain a half-game behind the Astros (80-61) for the AL West lead, with the Rangers (76-63) 2 1/2 games behind Seattle, as both Texas and Houston were idle on Thursday. The Mariners are in the second Wild Card position, two games ahead of the likewise-idle Blue Jays (77-63), with Texas a half-game behind Toronto for the final spot. The Mariners are also within 5 1/2 games of the Rays for the top Wild Card spot.

“They asked me before the game if I was ready to go in there, and I said, 'Yes, of course,'” Muñoz said. “I have to thank [the coaching staff] for all the help that they've given me in the past [after] outings that I've had that were tough outings for me, and giving me the confidence to be there in the ninth inning.”

The Mariners believe that they’re built to win these types of games, and they did lead MLB in one-run victories each of the past two years. But winning a 1-0 game on the road in a ballpark to which they could very well return for the AL Wild Card Series in four weeks makes this a far more significant win than most of their other 78 this year.

“You get into the playoffs or deep into September, you're going to have nights where it's just tough,” Mariners manager Scott Servais said.

The Mariners explicitly don’t label a “closer,” but much has justifiably been made about Muñoz being thrust into the highest-leverage pockets since the club dealt Paul Sewald at the Trade Deadline.

Muñoz this week was named AL Reliever of the Month for August, but he also had two blown saves and a loss in that stretch. And he began September by allowing an earned run in each of his first three outings, including Tuesday’s walk-off loss in Cincinnati, when he was on the mound for the final at-bat.

Yet as Servais’ usage has indicated for a heavily taxed bullpen on this road trip, at this time of year, it’s all hands on deck -- particularly with Seattle's highest-leverage arms.

“That's a tough role -- the last three outs are the hardest outs in the game,” Raleigh said of Muñoz. “Sometimes people forget that. Closing games is not easy, especially a one-run ballgame against one of the best teams in the league. He did great.”

Beyond Muñoz, Matt Brash also pitched for the third day in a row, though for him it was the first time since April 28-30 in Toronto. He worked his first 1-2-3 inning since Aug. 17, as he retired Tampa Bay's No. 3-5 hitters (Randy Arozarena, Josh Lowe and Isaac Paredes) in order in the eighth, turning almost exclusively to his slider for 12 of his 14 pitches.

Brash followed Isaiah Campbell, who put together perhaps the most dominant outing of his rookie season, with six whiffs among the 12 swings he generated to pick up three strikeouts while working around a two-out error from Josh Rojas, who had a tough night both at the plate and in the field.

The bullpen was all set up thanks to six scoreless innings from Luis Castillo, who became Seattle’s first starter since Tommy Milone on July 5 to issue four walks. Mariners starters have walked three or fewer in 135 of their 140 games, best in the Majors, and Castillo was able to overcome that shaky command early (along with 24 foul balls) to reach back for eight strikeouts and just four hits allowed.

After beginning the year 9-12 behind “La Piedra,” the Mariners have now won each of his past eight starts -- a promising trend given the time of year and how much he relishes pitching in October.

The Mariners entered this series with the AL’s third-hardest remaining strength of schedule (.525 win percentage) behind only the Red Sox (.550) and the Rays (.547), and if they reach October, it will be even more challenging. But Thursday’s victory showed that they seem to be up for this stretch run.