It’s customary at Yankee Stadium to always be looking up. You’ve got your Yankee Stadium short-porch specials and your Aaron Judge specials, moon shots that should be re-entering the atmosphere any day now. It’s enough to make them seem unstoppable — until, that is, you consider the big liability that has the potential to send them crashing down to Earth.

While it’s no secret that starting pitching was never going to be this team’s primary strength, the four-game series against the Astros was clear evidence that the Yankees have a problem that may soon need addressing. They dropped three of four games against the team with the best record in baseball, and their starters pitched to a 9.72 ERA in that stretch, thanks primarily to two weak performances from Luis Severino and Masahiro Tanaka on Sunday.

Their starters have a 4.20 ERA this season, and Tanaka and CC Sabathia have looked particularly inconsistent and vulnerable, respectively. The Yankees do have a host of options: GM Brian Cashman has said previously that, if deemed necessary, the team would be open to dealing for starting pitching but said Monday afternoon he’s not at the concerned stage with those two veterans.

“Obviously we need to get CC and Tanaka going in the right direction,” Cashman said. “But they’re pros and I have great belief they’ll get it ironed out.”

Of the rotation overall, Cashman repeated what he said from the time the club reported for spring training in February.

“It was the biggest question for us,” he said. “Hopefully we get what we want out of all of them.”

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Their top pitching prospect, Chance Adams, was also just promoted to Triple-A Scranton/Wilkes-Barre after pitching to a 1.07 ERA over 35 innings in Double-A.

While Aroldis Chapman’s shoulder injury falls squarely into the “bad news” category, Dellin Betances has proved he can handle the closer role, and the optimistic types will say it’ll be a good opportunity for Chad Green, called up to fill a long reliever role.

However, if that’s too much optimism, there’s the stark reality that none of those possibilities fix what’s going wrong now.

“No split, no sink,” manager Joe Girardi said when evaluating Tanaka’s performance in the second game of the Sunday doubleheader.

The righty, still pitching with a partially torn ligament in his elbow, allowed a career-high eight runs in 1 2⁄3 innings. Girardi said there was no indication Tanaka was injured, and Tanaka afterward said he wasn’t. (Not that it means all that much. Chapman didn’t tell the Yankees he was hurting, either, and Girardi said his closer was OK right up until he was placed on the 10-day DL on Sunday.)

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“He didn’t have either one of them tonight,” Girardi said of Tanaka’s splitter and slider. “I can’t tell you why, but his split had no depth to it. The slider was really kind of nonexistent and it’s tough to pitch that way . . . We’re trying to figure it out. He’s had some really good starts and he’s had starts where he hasn’t fared too well and [Sunday] was one of them. He gave up a number of home runs [four].”

Tanaka was booed heartily by the crowd when he exited, something he said he understood. “I didn’t get my job done, so, you know, they have all the right to,” he said through a translator.

His ERA jumped up to 5.80, highest in the rotation, and one of the worst marks in the league for qualifying starters. Before Sunday, he had won his last five starts, in no small part due to the Yankees’ American League-leading 201 runs.

“There are times like this during the season and you’ve just got to battle through it,” said Tanaka, adding that he doesn’t believe his struggles are due to the “mechanical flaw” he identified earlier in the season. “I think that has been fixed. I think it’s something different . . . think I have to kind of go look at some stuff and sort of analyze what I did.”

Sabathia, who will start Tuesday night in Kansas City, has had woes of a different kind. He’s struggled the first time through the order, pitching to an 8.14 ERA during the first three innings, and has experienced a steep decline since his first three starts. He’s had trouble locating his cutter and, thanks to his diminished velocity, opposing batters are hitting the ball with authority whenever he does miss his spots.

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Over 46 percent of batted balls were considered hard contact in his May 3 start against the Blue Jays, according to FanGraphs, a season high for him. He fared a little better in his last start against the Reds, finding better placement in the later innings, but still allowed five earned runs over six innings.

Girardi, though, isn’t worried — he said as much a few times over the weekend.

“Our starting pitchers had a tough time in this series,” he said. “We gave ourselves a shot [with their offense] . . . It wasn’t how we wanted this series to go, but to me, we had a chance in three of the four games . . . Keep getting those shots and we’re going to be all right.”

The question is, for how long?

With Erik Boland