HOUSTON -- With nine extra-inning games and 20 one-run games on their 57-game ledger, the Astros are approaching dangerous territory with regards to wearing out their effective, deep and versatile bullpen.

But with each close-and-late victory, those concerns seem mitigated.

Shortstop Carlos Correa lined a walk-off single to right field in the 12th inning and the Houston Astros claimed a 6-5 victory over the Oakland Athletics on Saturday at Minute Maid Park.

Houston (27-30) improved to 6-3 in extra-inning games and 9-10 in one-run affairs thanks in large part to a bullpen that worked 3 1/3 scoreless innings after closer Luke Gregerson blew the save in the ninth.

"We carry 13 pitchers for a reason and part of that is to relieve some of the stress on the pen," Astros manager A.J. Hinch said. "We'll monitor it. I certainly don't love taxing the bullpen to this extent, but in these close games the guys are stepping up to do their jobs."

Right fielder George Springer opened the 12th with a double to right against Athletics closer Ryan Madson (2-2) and advanced to third base when Jose Altuve followed with a sacrifice bunt. Correa jumped on the first pitch as Houston won for the 10th time in 12 games.

That late rally served as a contrast to the eighth inning when the Astros squandered an insurance opportunity while leading 5-4. Correa drilled a leadoff triple to right-center field yet was left stranded on third base when Oakland left-hander Sean Doolittle rallied to strike out Colby Rasmus and Luis Valbuena, both left-handers, plus Marwin Gonzalez.

Four innings later, those struggles were long forgotten.

"The feeling's good," said Rasmus, who finished 2-for-4. "We knew we were a good team from the beginning. Hopefully we've got some of those bumps in the road kind of out of the way and just kind of feeling out who we are as a team and I think everything's coming together.

"We're pitching, we're getting those hits when we need to get them. Obviously George and Altuve leading the pack, getting on base all the time and swinging the bats the way they're doing is definitely picking up the rest of us and putting pressure on those pitchers."

Athletics second baseman Jed Lowrie rallied Oakland (25-31) by slapping his first home run on the season with two outs in the ninth inning against Gregerson, who blew his second consecutive save.

Excluding Gregerson, five Houston relievers allowed six hits and one walk with five strikeouts over six scoreless innings. Right-hander Scott Feldman (3-3) earned the win pitching around a single in the 12th.

The Astros responded to the Athletics' three-run second inning with three runs of their own in the bottom of that frame. Evan Gattis had the biggest blow in the rally, drilling a 2-2 pitch from Athletics starter Kendall Graveman 381 feet to left field. Gattis' eighth homer followed Rasmus' leadoff double and cut the deficit to 3-2.

Graveman allowed five runs, seven hits and one walk in 4 1/3 innings. His brief outing again forced Oakland to dip into its bullpen early.

"We've been dealing with that all year," Athletics manager Bob Melvin said. "We have an off day the day after tomorrow, so we will get through it."

Khris Davis and Yonder Alonso followed a leadoff walk by Danny Valencia in the second with singles that loaded the bases with no outs against Astros starter Collin McHugh, who later allowed a two-run double to Chris Coghlan and a sacrifice fly to Josh Phegley that gave the Athletics a 3-0 lead.

Valencia added his ninth homer in the sixth. Oakland outhit the Astros 12-10 but stranded 11 and hit 2-of-11 with runners in scoring position.

"We gave ourselves some opportunities," Lowrie said. "We also pitched out of some big spots, too. They had plenty of opportunities. Unfortunately, that is the way that a lot of these extra-inning games go. The home team has the advantage."

NOTES: Athletics RHP Sonny Gray will return from the 15-day disabled list and pitch the series finale against the Astros on Sunday. Gray was placed on the DL on May 21 because of a strained right trapezius. He will skip his scheduled rehab start for High A Stockton to rejoin the Athletics. ... Athletics LHP Rich Hill, scratched from his start on Saturday because of a mild groin strain, could return for the Reds series June 10-12. ... Astros C Jason Castro returned to the starting lineup after missing four games because of an illness. ... Athletics LHP Daniel Coulombe was recalled from Triple A Nashville to replace RHP Andrew Triggs, who was optioned to Nashville. Coulombe joins the Athletics, for whom he has a 4.76 ERA in three appearances, for the third time this season. Triggs posted an 8.00 ERA in 10 relief appearances with the Athletics.