The first variable in the Yankees' playoff-clinching scenario Tuesday night at the Stadium involved beating the Red Sox, but the visitors hung up a six-spot against Michael Pineda in the first inning, pretty much rendering all the other playoff variables moot right off the bat.

The larger question after a 10-4 loss that left the Yankees' magic number for a wild-card berth at two was how their starting pitching will hold up in the postseason. Pineda (12-9, 4.24 ERA) at least showed the fortitude to pull himself together and allow only one run over his final five innings, but his wildly inconsistent outing didn't inspire confidence.

That makes Wednesday night's return of ace Masahiro Tanaka from a hamstring injury all the more important, especially since Joe Girardi already has indicated he will start the wild-card playoff next Tuesday. If they win and advance, Girardi then faces a tough decision choosing among rookie Luis Severino, the faded CC Sabathia and the up-and-down Pineda to lead off the rotation in the Division Series.

Describing Pineda's performance, Girardi said: "He looked like his stuff was up and flat. He seemed to find it after that, but they jumped all over him . . . We got it to 6-4, so it was definitely manageable."

Pineda's slider didn't fool anyone in the first inning. Mookie Betts led off with a double, Dustin Pedroia singled and Xander Bogaerts reached on a fielder's choice that scored Betts. Then David Ortiz doubled on a ball rightfielder Carlos Beltran misplayed off the wall, moving Bogaerts to third.

Pineda fielded a chopper by Travis Shaw and threw home, but Bogaerts beat the tag to score Boston's second run. A double by Brock Holt drove in Ortiz, and then Blake Swihart cranked a 94-mph fastball into the rightfield seats for a three-run home run and a 6-0 lead.

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Still with only one out, Pineda was dangerously close to being lifted right there. According to Elias Sports Bureau, it was the most runs the Sox ever scored in the first inning of any of their 837 games at the Stadium.

But Pineda suddenly steadied to get the final two outs of the first to start a stretch in which he retired 11 straight batters. By the time he returned to the mound for the second, it was a game again thanks to a four-run first by the Yankees.

"I feel a little mad, a little angry," Pineda said. "I ruin the first inning, but I have to keep pitching. I keep trying to attack the hitter and be a little more aggressive . . . I adjusted after the first inning and threw the ball well."

The Yankees' four-run first began with a double by Jacoby Ellsbury, a Brett Gardner single and a run-scoring groundout by Brian McCann. Beltran doubled Gardner home, and then Dustin Ackley crushed a pitch by Rick Porcello (9-14) into the rightfield stands to cut the Yankees' deficit to 6-4.

Taking his cue from Pineda, Porcello proceeded to string zeros across the scoreboard. He got a cushion from a solo homer by Betts in the fifth inning, and Swihart added a two-run shot off Bryan Mitchell in the eighth. The Yankees' bats had nothing left after the first inning.

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"Porcello dominated me all night basically with one pitch -- the sinker," said Alex Rodriguez, who was 0-for-4 with two strikeouts. "But I like our team a lot, I like where we're at. We just need to relax."