Yankees pitcher J.A. Happ hands the ball to manager Aaron...

Yankees pitcher J.A. Happ hands the ball to manager Aaron Boone, left, as he is removed during the fifth inning of a game against the Athletics on Wednesday in Oakland. Credit: AP/Ben Margot

OAKLAND, Calif. — J.A. Happ has enjoyed far more success than not in his 13-year big-league career, which includes plenty of postseason experience.

But at some point, the 36-year-old lefthander is going to have to show the Yankees he’s worthy of being trusted with a playoff assignment this October.

The clock is still ticking.

Facing a team who well could be a playoff opponent, Happ again was victimized by the long ball Wednesday night, allowing two homers over four-plus unimpressive innings of the Yankees 6-4 loss to the A’s in front of 22,017 at Oakland Coliseum.

“Struggling to keep the ball in the park for whatever reason,” said Happ, whose fastball, always his calling card, once again let him down, the case most of this year. “It’s not for lack of trying to figure it out. We’re trying to do everything we can between starts to figure out sequencing, location, execution, even delivery. But they got the two today and they had a guy on base each time and that makes it tough.”

Happ (10-8, 5.58) allowed five runs and five hits in his outing, a line that would have been worse had Chad Green not taking over with none out and the bases loaded in the fifth and given up just a sacrifice fly.

The two homers gave Happ, who shook off catcher Gary Sanchez significantly more than in previous starts, 31 allowed in 25 starts this season. His previous high was the 27 homers allowed in 31 starts last season when he went 17-6 with a 3.65 ERA, including 7-0 with a 2.69 ERA with the Yankees.

“I feel like I have the same stuff,” Happ said, comparing this season to last. “It seems similar to me. So that’s part of the process of trying to figure out why the results haven’t been there.”

Of shaking off Sanchez, who wanted more offspeed pitches, Happ said the pair weren’t on the same page “maybe not as much as we have in the past but that’s really nobody’s fault. I just think sometimes we’re thinking differently out there.”

Sanchez didn't mind.

“That’s part of the game, that’s part of baseball, it’s part of being a pitcher and being a catcher in the big leagues,” Sanchez said through his interpreter.

The Yankees (83-45), who have lost the first two games of this nine-game, three-city trip west, made it interesting late, pulling within 6-4 after trailing 6-2.

But with runners at the corners and one out in the eighth — an inning started by touted lefty A.J. Puk — righthander Liam Hendriks struck out DJ LeMahieu and Aaron Judge, who both finished 0-for-5 in the game. Judge’s slump continued as the righthander is in a 9-for-54 skid. The Yankees, after going 0-for-5 with runners in scoring position and stranding eight Tuesday, outhit Oakland 11-6 and went 3-for-9 with RISP Wednesday but stranded 10.

“A lot of good at-bats,” Aaron Boone said. “Couldn’t quite break through to make it a real dynamic offensive night, but 11 hits so a lot of things happening good up and down the order. Just not that big hit tonight.”

The A’s (73-53), who saw Hendriks work a perfect ninth for his 15th save, improved to 23-12 since the All-Star break.

After Happ retired the A’s in order in a 17-pitch first the pitcher’s offense gave him a lead.

Didi Gregorius doubled to lead off the inning and, after Gleyber Torres grounded out, Mike Tauchman bounced a full-count curveball to right, the RBI single making it 1-0.

Happ could not duplicate his success in the bottom half of the second. He struck out Mark Canha with a fastball to start the inning, then retired Chad Pinder on a comebacker. But Stephen Piscotty singled back up the middle and Khris Davis snapped a 0-for-17 slide by taking a full-count 94-mph fastball the other way, his 18th homer making it 2-1.

Mike Fiers (12-3, 3.46), who allowed two runs and six hits in 5 1/3 innings, quickly got his offense back to the plate with a 1-2-3, 11-pitch top of the third.

Josh Phegley, the No. 9 hitter, worked a leadoff walk in the bottom half and Marcus Semien pounced on a hanging 1-and-1 slider and hammered it to left-center, the shortstop’s 22nd homer making it 4-1. The blast improved Semien to 9-for-21 with three homers in his career vs. Happ.

The Yankees put two on with two outs in the fourth against Fiers — Tauchman singled with two outs to put runners at the corners — but Cameron Maybin struck out swinging.

After retiring the A’s in order in the fourth, Happ did not survive the fifth. Jurickson Profar led off with a double to left and Happ hit Phegley in the shoulder area with a 92-mph fastball. He then walked Semien and Boone saw enough, calling on Green to face Chapman. Green got ahead of the third baseman 1-and-2, eventually getting him to foul out to third (Urshela caught the pop up near the A’s dugout and was knocked to the ground by Sanchez, who was also in pursuit of it). Green quickly got ahead of Matt Olson, who homered the night before, getting him to foul out to Urshela as well.

Oakland would get one in the inning when Mark Canha sent a grounder to the hole where Gregorius couldn’t pick it clean, the infield single bringing in Profar to make it 5-1.

“Tonight was a little bit what’s happened to him throughout the season,” Boone said. “You see a lot of good in there . . . I know he’s frustrated obviously. We just have to keep grinding away. The stuff is there enough for him to go out and be successful. We have to continue to try and find a way with him.” 

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