OAKLAND, Calif. — That five-game winning streak that seemed to resolve all the Yankees problems has been followed up by back-to-back losses to the worst team in the American League that’s in the midst of a fire sale. 

And while Clarke Schmidt was unimpressive in his second start of the season, more worrisome is a lineup that came up nearly empty against the A’s in a 4-1 loss in front of a crowd of 29,498 at the Oakland Coliseum. 

The Yankees were held to three or fewer runs for a third game in a row, despite facing a starting pitcher with an ERA over 6.00 for the second straight game. 

And since the Rays beat Boston on Sunday, the Yankees’ lead in the AL East dropped to 7 ½ games. 

“The last 22-plus hours have not been very good for us offensively,” manager Aaron Boone said. “We’ve got do a better job.” 

Asked if it was difficult for his first-place team might have taken the cellar-dwelling A’s lightly, Boone said, “This time of year, we’re trying to win a division and we’re getting down to stretch time, so we better not [be]. We have to make sure to bring it every single day. I don’t think that’s the issue. We just got shut down.” 

After being one-hit in an 11-inning loss on Saturday, the Yankees didn’t get a hit on Sunday until Aaron Hicks drilled a single to center with two outs in the fifth. 

Hicks scored on Kyle Higashioka’s base hit to cut the Yankees’ deficit to 4-1, but that was all they got, as Andrew Benintendi then sent a shot to the wall in left, where Tony Kemp made a good catch to end the inning. 

Prior to those singles, the Yankees were held to one hit over 17 innings, starting in Friday’s win. 

Oakland’s rookie right-hander, Adrian Martinez, limited the Yankees to one run in 5 ¹/₃ innings in just the sixth start of his career. 

Schmidt, meanwhile, was hit hard throughout his outing. 

He gave up four runs on eight hits in just 4 ¹/₃ innings and struggled from the early part of the game, as he gave up a pair of runs in both the first and third innings. 

Former Yankee prospect Dermis Garcia — who spent last season at Double-A Somerset — had an RBI single in the first to make it 2-0. 

Schmidt’s woes continued in the third, with a leadoff double to Nick Allen, who scored on Kemp’s single through the left side of the infield. Garcia added another RBI later in the inning with a grounder up the middle to put the Yankees in a 4-0 hole. 

He gave up eight hits in the first three innings, but Boone said he’d remain in the rotation — although with an off day on Thursday, their plans are undetermined for later in the week. 

Both Schmidt and Boone lamented Schmidt’s inability to put batters away, especially with two strikes. 

After the Yankees scored in the fifth, they threatened again in the sixth — but failed to score. 

Giancarlo Stanton singled to left with one out to knock Martinez out of the game. 

Facing left-hander Sam Moll, Anthony Rizzo squibbed a base hit down the third-base line to put runners on the corners with one out. 

But DJ LeMahieu grounded into a double play. 

Anthony Banda, signed to a major league contract and added to the roster on Sunday, took over for Schmidt in the fifth and Greg Weissert, coming off his rough MLB debut on Thursday, pitched a scoreless sixth and seventh, retiring all six batters he faced. 

Hicks walked with two outs in the seventh and moved to second on a passed ball. Higashioka grounded out to end the inning. 

“Just the other night, we had 20 hits, so we’re not too far off,” Aaron Judge said, referring to the 13-run outburst on Thursday against the A’s. “This time of year is kind of a grind and this team knows that. We got our butt kicked and now we have to respond in Anaheim.”