HOUSTON — The Yankees followed up their most impressive victory of the season with perhaps their most frustrating 2017 defeat.

After rallying from a two-run deficit to take a pair of three-run leads, the Yankees saw their top two relievers flush it away in a 7-6 loss to the Astros on Saturday night in front of a noisy sellout crowd of 41,010 at Minute Maid Park.

Losing pitcher Dellin Betances, the culprit in a brutal loss Tuesday night in Chicago against the White Sox, allowed one hit and three walks and was charged with four runs in two-thirds of an inning Saturday night. Yuli Gurriel’s two-out, two-run double on a 100-mph inside fastball from Aroldis Chapman capped a four-run eighth for Houston that erased the Yankees’ 6-3 lead. It was the Yankees’ 15th blown save of the season.

“It’s tough,” said Betances, who walked two and allowed a hit in two-thirds of an inning Tuesday. “These guys fought to come back. [Jordan] Montgomery had a really good start, hitters did what they did. I didn’t do my job and that’s the reason we lost.”

Ken Giles pitched a scoreless ninth for his 19th save. Brett Gardner singled with two outs but had thoughts about stretching it into a double to get into scoring position and was thrown out at first after taking too wide of a turn.

“You have to think second base on that,” Joe Girardi said, not taking issue with the aggressive turn. “It ends up being the wrong read, but those are split-second decisions that a baseball player has to make.”

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The Yankees (43-36), losers of 13 of 18, fell two games behind the AL East-leading Red Sox.

The poor outing by Betances wasted Didi Gregorius’ first career grand slam and a memorable big-league debut by Clint Frazier. Getting the start in place of rightfielder Aaron Judge, who pinch hit for Chris Carter and popped out for the first out of the ninth, Frazier, 22, homered in the seventh to give the Yankees a 6-3 lead and also doubled.

“It’s probably the best taste of baseball I’ve ever had,” said Frazier, who initially received the silent treatment from his teammates, often a tradition with rookies after their first homer. “Disappointing to lose, but I’m just glad I got to be a part of this game.”

According to a source, Frazier got the home run ball back in exchange for four balls he autographed . . . and one signed by Judge.

Judge homered in his first career game last season and predicted he might see it again from Frazier. “I think he might,” Judge said beforehand. “I’ve got a good feeling for him tonight.” He was right.

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Frazier’s double helped jump-start a five-run sixth inning that turned a 2-0 deficit into a 5-2 lead. After an RBI single by Gary Sanchez produced the first run, Gregorius’ grand slam gave the Yankees the three-run lead.

Montgomery, the rookie lefty who entered the game 4-1 with a 2.34 ERA in his last seven starts, allowed three runs and five hits in 5 1⁄3 innings Saturday night, giving up a two-run homer by Gurriel in the fifth and a solo shot by Carlos Correa in the sixth that made it 5-3.

Betances was an immediate mess, walking Jose Altuve with one out and hardly holding him on as he stole two bases. After Correa’s RBI grounder made it 6-4, Evan Gattis’ titanic homer to left moved the Astros (55-27) within 6-5.

After two more walks issued by Betances, Chapman gave up Gurriel’s two-run double, pulled down the third-base line, on a 3-and-2 pitch.

“You have to give him credit,” Chapman said through his translator. “I think his mind was set to hit something inside fast. I think he was looking for it and was ahead of the pitch.”

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Betances, who described himself as “breaking ball- happy” in Chicago, didn’t fix that Saturday night, though he didn’t have a feel for his fastball either.

“I feel like I’m just not commanding both my pitches,” he said. “I give up one hit today and they score four runs. That can’t happen.”