OAKLAND, Calif. — One good outing by Masahiro Tanaka at the start of this trip west didn’t fix him after all.

It wasn’t one step or even two steps back Saturday afternoon against the A’s for the righthander in a 5-2 loss in front of 31,418 at Oakland Coliseum, more like three or four.

Tanaka’s outing was the biggest factor in the Yankees’ fifth straight loss, which dropped them to 38-28 overall and 1-5 on a trip that started with Monday’s victory over the Angels and ends Sunday against the A’s (30-38).

If the Red Sox beat the Astros Saturday night, they would pull into a tie with the Yankees atop the AL East, though it’s far too early to watch the standings.

“We’ll be glad to head back east after the game,” Brett Gardner said. “But we do have one more game here tomorrow and it’s an important game.”

Tanaka allowed a home run on the first pitch he threw, one of three bombs he surrendered over four innings of an odd afternoon that also included him striking out 10.

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“Three home runs, that’s unacceptable,” Tanaka said through his translator. “I felt like I was able to get a couple of good strikeouts, which tells you there’s some bite to the offspeed stuff, so I look at that as a positive from today’s outing.”

Still, trouble with the longball has been a persistent problem.

The 28-year-old has allowed 21 homers this season, one shy of the total he gave up last year. Tanaka, now 5-7 with a 6.34 ERA, has allowed 15 homers in his last seven games.

According to researcher Katie Sharp, Tanaka became the only MLB pitcher in last 100 years with 10 or more strikeouts and three or more homers allowed in an outing of four innings pitched or fewer.

“It’s very frustrating,” Tanaka said before referencing a bullpen that’s been taxed all week. “Obviously I wanted to go deep into the game and eat up some innings and I wasn’t able to do that.”

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After allowing a homer to Matt Joyce on the first pitch he threw — a belt-high 91-mph fastball — Tanaka struck out the next three, all swinging on splitters, giving the appearance he had settled in, much as he did Monday in Anaheim when he allowed a homer to Kole Calhoun, the game’s second batter. It was the only earned run he allowed that night over 6 2⁄3 innings.

The Yankees even gave Tanaka a lead with two runs in the second but it did not last.

The A’s tied with one out in the bottom half when Tanaka hung a 1-and-2 splitter that Ryon Healy launched to left-center for his 16th homer of the season and first of two blasts in the game for the Oakland DH.

“You make mistakes in this game, guys are going to make you pay,” Austin Romine said. “It doesn’t seem like he can get away with much right now either. It’s just falling really good for him.”

The Yankees had taken a 2-1 lead in the top half, getting an RBI single by Romine and a Gardner sacrifice fly. The A’s tied with one out in the bottom half when Tanaka hung a 1-and-2 splitter that Ryon Healy launched to left-center for his 16th homer of the season.

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Healy led off the fourth by driving a flat full-count splitter to deep left-center to give the A’s a 3-2 lead.

Matt Chapman, a rookie called up Thursday who provided the go-ahead hit Friday night, followed with a single. Tanaka struck out Jaycob Brugman and Josh Phegley but Joyce singled and Adam Rosales dumped a 1-and-1 fastball to right, the RBI single making it 4-2. Jed Lowrie beat out an infield single to second to make it 5-2. After Romine’s one-out RBI single in the second, the Yankees went without a hit until Starlin Castro’s two-out single in the eighth. Aaron Judge, again with a large group of friends and family in attendance (he’s from nearby Linden), had one of his roughest games of the season, going 0-for-3 with a walk and three strikeouts.

Oakland righthander Jesse Hahn (3-4, 3.56) allowed two runs, three hits and three walks over five taxing innings in which he threw 105 pitches.

Lefthander Sean Doolittle pitched a scoreless ninth for his second save.

“We’re just not getting the job done,” Judge said. “Frustration? Yeah, no one likes to lose. We want to go out there and win every game. But it’s a long season. You’re going to have those times where you have a little skid like this. It happens. But we’re still fighting, we’re still battling.”