NEW YORK >> A rainy day in the Bronx has left a most daunting October test for the New York Yankees vaunted bullpen: four games, four days and already a deficit to overcome against the Houston Astros in their AL Championship Series.

Game 4 of the ALCS scheduled for tonight was postponed a day because of poor weather, with Game 5 pushed to Friday night at Yankee Stadium and Games 6 and 7 in Houston on Saturday and Sunday, if necessary. The Astros beat New York 4-1 on Tuesday to take a 2-1 series lead.

The winner will face Washington and its well-rested, talented rotation starting in the AL city on Tuesday night.

With New York relying so heavily on its relievers this month, the starter-driven Astros may be at an advantage.

“If we’re going to win this series, our bullpen will still play a huge role, obviously,” Yankees manager Aaron Boone said. “But we’ve got to be able to get a little bit of distance out of our starters.”

Houston will pitch Zack Greinke on Thursday against the Yankees’ Masahiro Tanaka in a rematch of Game 1, both on regular rest. Tanaka pitched six sterling innings as New York won 7-0.

The Astros also announced that Justin Verlander will start Game 5 on full rest. He threw two-run ball into the seventh inning in a 3-2, 11-inning victory in Game 2 on Sunday.

“It was an easy decision,” Astros manager AJ Hinch said.

New York plans to counter Verlander with James Paxton. The left-hander was pulled after allowing a run over 2 1/3 rocky innings in Game 2, and concerns were raised that he was tipping his pitches.

Both clubs had planned to use openers today, and New York will almost certainly still use a bullpen day in the series, probably in Game 6.

Boone has ridden his relievers hard, asking them to cover 15 1/3 out of 28 innings in the series — a tough enough task with October’s built-in days off. The rainout leaves Aroldis Chapman, Zack Britton and the rest of that group without some valuable recovery time.

Tanaka has been New York’s best bet for length this postseason. He needed just 68 pitches to cover six innings in the opener, improving to 5-2 with a 1.32 ERA in the postseason.

“Anytime the moment gets really big, he is good at slowing the game down himself and maybe taking even a little bit off of his pitches as opposed to powering through it,” Hinch said. “We’d like to see us have a more disciplined approach, but that’s easier said than done with the stuff he has.”

Greinke, a 2009 Cy Young Award winner acquired from Arizona at the July 31 trade deadline, has struggled through two starts this postseason. He allowed six runs and couldn’t finish the fourth inning against Tampa Bay in Game 3 of the AL Division Series, and the Yankees hammered two homers and scored three runs against him in six innings in the ALCS opener.

The Astros may also lean heavily on relievers in Game 6, if necessary, although their bullpen strategy will differ from New York’s. While the Yankees probably wouldn’t ask any one pitcher for more than two or three innings, Houston could stretch starter José Urquidy over four or five innings after an opener. That could keep the rest of the club’s arms fresher during this four-day run.

“How beneficial it is is probably easier to answer after I see how guys perform and how the pitching plays out,” Hinch said of the rainout. “But like I said, it’s kind of a wait and see.”

The previous postseason game to be postponed was Game 4 of the 2017 NL Division Series between the Nationals and Cubs.

STANTON’S STATUS

Boone remained uncertain today if slugger Giancarlo Stanton would return to the lineup in Game 4. Stanton was held out of Games 2 and 3 after straining his right quad in the opener.

Stanton was set to receive treatment. Boone said he was available to pinch hit Tuesday.

“I’m not really close to making that decision yet,” Boone said. “That will be something that we kind of work through today and possibly even into tomorrow.”

Boone said it was likely that Aaron Hicks will be in the lineup regardless. The center fielder made his first start Tuesday since Aug. 3 due to an elbow injury and went 0 for 2 with two walks.

Boone also doubled down on his vote of confidence for struggling catcher Gary Sanchez, who is 2 for 21 this postseason. Sanchez was booed and criticized Tuesday when he couldn’t block a wild fastball from Britton, allowing a run to score.

“He’s been excellent behind the plate from a game-calling standpoint, from a game-plan target, receiving,” Boone said. “A lot of people are making a lot of the block. There’s a lot of 94 mph fastballs that guys don’t block. Guys aren’t always set up to block a fastball. That’s kind of a 50/50 play.”

NEW CREW

Mike Everitt will replace Jeff Nelson as umpire crew chief for the remainder of the ALCS after Nelson was removed from Game 3 with a concussion. Nelson took two foul balls off his mask before Kerwin Danley swapped in behind home plate. Everitt was the plate umpire for the NL wild-card game this season.