SEATTLE -- To a player, the Astros said they approached Wednesday’s series finale against the Mariners as a must-win. Considering the season is in its final days and a loss would have slid them out of the playoff picture, the Astros’ urgency was certainly warranted.

The Astros took a major step toward their seventh consecutive postseason berth Wednesday night by getting a clutch three-run homer from center fielder Mauricio Dubón and five scoreless innings from their bullpen to beat the Mariners, 8-3, at T-Mobile Park in one of their biggest regular-season wins in years.

“I guess this was a must-win,” said closer Ryan Pressly, who recorded the final four outs. “We approached it like a playoff game, there was a little bit of a playoff atmosphere out here and we kind of felt at home a little bit.”

• Games remaining (3): at AZ (3)
• Standings update: The Astros (87-72) are in second place in the American League West, 2 1/2 games behind the Rangers (89-69). Seattle (85-73) is 1 1/2 games behind Houston for the third and final AL Wild Card spot. The Astros hold the season tiebreaker against the Rangers, but not the Mariners.

By taking two of three games from the Mariners, the Astros moved 1 1/2 games ahead of Seattle for the final Wild Card berth in the American League, with Houston having three games remaining this weekend at Arizona. If the Astros sweep the D-backs, the Mariners can’t catch them.

Every Astros starter had at least one hit, with Michael Brantley -- playing for the first time in nine days -- going 4-for-5. Yordan Alvarez and Martín Maldonado also clubbed homers for the Astros, and Jose Altuve recorded his 400th career double in the fifth inning.

“We think this game was huge,” Maldonado said. “Everybody was talking today that we’ve been here before in this situation -- a must-win game. We went out there and executed from the first at-bat. We followed our game plan and we got the W. We have to take the same thing to Arizona.”

Alvarez tied the game at 1 with a Statcast-projected 442-foot homer to center field to lead off the fourth inning, and Dubón hit a three-run homer off Mariners starter Bryce Miller later in the inning for a 4-1 Houston lead. Dubón’s 10th long ball gives the Astros 11 different players with double-digit homers.

“Got us ahead against a good pitcher,” Dubón said. “It’s been a crazy year. Down to the last three games. It’s a pretty good swing.”

Astros starter Framber Valdez flirted with disaster in the first inning, giving up a leadoff homer to J.P. Crawford on his second pitch of the night and walking the next two batters. Valdez was visibly upset at some balls he thought were strikes, and pitching coach Josh Miller and Maldonado tried to settle him down.

Valdez wound up going four innings, allowing three runs on five hits and five walks while striking out seven batters, giving him 200 strikeouts for the season -- the first such year of his career.

Valdez joined Dallas Keuchel (2015) and Mike Cuellar (1967) as the only lefties in club history to reach 200 in a season.

“The strike zone was moving all around for Framber early, but luckily we had Maldy back there to direct him,” Astros manager Dusty Baker said. “He only gave up one run in that inning. I think it was a 30-pitch inning or something like that. We had the crooked-number inning in the fourth. He got out of trouble again. He was sharp at times and not sharp at other times, but we got some big hits in there.”

The Astros-Mariners rivalry bubbled up in the sixth, when Hector Neris struck out Julio Rodríguez to end the inning and the two exchanged words. Benches emptied, and the Astros answered by scoring three times in the seventh inning on RBI hits by Kyle Tucker, José Abreu and Brantley to take a 7-3 lead they wouldn’t relinquish. 

Kendall Graveman (one inning), Neris (one inning), Bryan Abreu (1 2/3 innings) and Pressly (1 1/3 innings) held the Mariners to three hits in the final five frames. Houston’s bullpen has posted a 0.67 ERA with 32 strikeouts in 27 innings in the team’s last seven games.

“The bullpen’s been our strength all year,” Maldonado said. “Everything you asked from [Bryan] Abreu was huge. He was getting a little tired. Those guys carried us all year and last year to the postseason. We weren’t expecting anything less, especially with an off-day [Thursday]. Those guys stepped up.”