Perhaps it should've come as no surprise that the longest scoreless game in Major League Baseball postseason history would be decided by one swing of the bat.

After all, that's essentially what every game of the American League Division Series between Houston and Seattle came down to.

Rookie Jeremy Pena, hitless in his first seven at-bats, homered leading off the 18th inning as the Astros eliminated the host Mariners in the ALDS with a 1-0 victory Saturday.

The Astros swept the best-of-five series 3-0, advancing to the ALCS for the sixth straight year and spoiling Seattle's first postseason appearance since 2001.

Houston will face either the New York Yankees or the Cleveland Guardians for a berth in the World Series.

Pena's homer, which just cleared the wall in left-center field on a 3-2 pitch from Mariners right-hander Penn Murfee, decided the marathon contest. Saturday's affair surpassed the 14 innings Cleveland and Tampa Bay played without a run earlier this month in the AL wild-card round.

Pena's clutch blast came after the Astros' Yordan Alvarez hit go-ahead home runs in each of the first two games of the series, including a three-run, walk-off shot in Game 1.

"We didn't know who the hero was going to be, but we were hoping that we would have somebody," Astros manager Dusty Baker said. "And we had somebody in Pena."

Pena took over at shortstop this season for the Astros after longtime standout Carlos Correa left in free agency.

"You never know until you get there, but you could tell by his brightness in his eyes and his alertness on the field that he wasn't scared and he wasn't fazed by this," Baker said. "Boy, he's been a godsend to us, especially since we lost Carlos, because this could have been a disastrous situation had he not performed the way he has. And he's only getting better. That's what you want."

Pena looked like he had been through a doubleheader, which in essence he had, by the time he sat down in the postgame interview room.

"I'm tired," Pena said with a laugh. "That was a long game. But in the playoffs, the crowd was into it the whole game, and shout-out to their fans and their team. They put up a great fight."

Astros right-hander Luis Garcia pitched five innings of two-hit ball for the victory. He didn't walk a batter and struck out six.

"To pitch extra innings like that, I mean, that was a start for him," Baker said. "When a guy comes out of the bullpen and he can go five innings or more ... it's a very secure feeling when you know that you have innings and you have quality in your bullpen."

The teams combined to strike out 42 times, strand 24 runners on base and went 0 for 19 with runners in scoring position. The game lasted 6 hours and 22 minutes before Houston prevailed.

"These guys, they know not to panic. They don't get too excited. They don't get too down. It means a lot," Baker said. "Once you've been through it and then you go through it again and again and again, and then you sort of expect excellence, and that's what this team expects out of itself."

The Astros didn't have a hit in extra innings until Alex Bregman's one-out single in the 16th off Matthew Boyd. Kyle Tucker walked, sending Bregman to second, and the Mariners brought in Murfee.

Yuli Gurriel hit a liner into the gap, but center fielder Julio Rodriguez made a diving catch to prevent the run from scoring. Murfee then got Aledmys Diaz to foul out to end the threat.

Seattle got a one-out single from Carlos Santana in the 12th, but he was erased on a double play.

Rodriguez walked with two outs in the 13th and stole second before Ty France grounded out to third to end the inning.

Mitch Haniger singled with two outs in the 14th, but Santana was caught looking at a third strike to end that inning.

Seattle's only other baserunner in extras came on Santana's two-out single in the 17th. He advanced on a wild pitch, but Adam Frazier popped out.

The game featured sterling efforts from starting pitchers Lance McCullers Jr. of Houston and Seattle rookie George Kirby.

McCullers allowed two hits through six innings with two walks and seven strikeouts. Kirby, making his first postseason start, went seven innings and gave up six hits, didn't walk a batter and struck out five.

The Mariners swept host Toronto in the wild-card round before suffering the same fate at the hand of the Astros, their AL West rivals.

"Yeah, a lot to unpack over the last six, seven hours, whatever it's been when this game started," Mariners manager Scott Servais said. "But really for me I cannot talk about anything unless I talk about the fans that were in the ballpark (Saturday). Wow. Some kind of impressive. ... We were right there. You look at the whole series, it really comes down to three swings of the bat. Certainly Yordan got us a couple times in Houston and Pena with a big one (Saturday)."

--Field Level Media