Can you temper expectations for a superhero?

Maybe it’s time to downgrade The Dark Knight — for the moment, at least — to … The Shady Apprentice?

Whether it’s because of the Tommy John surgery or because he just wasn’t going to match his high standards regardless of his health, Matt Harvey is no longer the Mets’ ace.

His humanness re-emerged at about the worst possible time Wednesday night, as, with his team trying to rebound from a no-hitter, he gave up a two-run lead and ultimately suffered an 8-5 pummeling that stunned the Citi Field crowd and knocked the Mets (31-29) out of the National League East penthouse.

“I’m just not doing my job very well,” said Harvey, whose ERA rose from 3.05 to 3.62. He owns a 7.20 ERA over his last four starts, although that can be attributed largely to two of the starts — Wednesday’s and May 23 at Pittsburgh.

In each appearance, he allowed seven runs, a career worst. He established other nadirs Wednesday by giving up three home runs and striking out just two. The nine homers he has permitted in 79 ²/₃ innings already is the most for one season of his career.

Beyond the raw numbers, Harvey betrayed his own narrative as the team’s stopper by giving up a 4-2 lead with a five-run sixth (his worst inning ever).

This when the Mets badly wanted a win after getting no-hit by Giants rookie Chris Heston Tuesday night, and when they began play knowing that they needed to win to stay in first place after the Nationals outlasted the Yankees, 5-4 in 11 innings, during a day game in The Bronx.

Is this the Tommy John hangover? That sure seems like a viable theory. After all, Harvey rested more than 17 months before making his first appearance that counted, and he cruised to a 1.98 ERA in his first eight starts of the campaign. Common sense dictated he couldn’t keep going at that rate. His manager buys into it.

“You’re looking at a guy tonight [who] threw 97 to 99 [mph],” Terry Collins said. “Pretty good swings. Two strikeouts and good swings. That just tells you, even though it’s hard, that little extra at the end may not be there.”

“I’m not going to use that as an excuse,” Harvey said, when offered the Tommy John lifeline.

Well, he pays his agent Scott Boras good money to use that as an excuse, although I like to think of it (and I bet Boras would agree) as more of an explanation than an excuse. Back in December, Boras told The Post: “The expectations of what the pitcher can do the next season [after the surgery] have limits, limits that may not be necessary the year following the surgery.”

Collins pointed out how the Giants’ big hits came on pitchers’ counts. St. John’s product Joe Panik cracked his first-inning, two-run homer on an 0-and-2 fastball. Buster Posey smoked an 0-and-2 fastball for a sixth-inning, two-run double. Justin Maxwell’s solo blast in the seventh came off an 0-and-1 two-seam fastball.

“With his stuff, you don’t get hit that hard when the ball’s in the middle of the plate,” Collins said. “This guy pounds the strike zone, but you’ve got to keep it out of the middle if you can.”

Catcher Travis d’Arnaud, who played in his first game since April 19, said that Harvey simply needed to work on his location, and maybe it’s that simple. Harvey repeatedly mentioned his desire to get right back to work on this, and you don’t doubt his work ethic or his competitiveness.

Before the game, Collins said, “We’re asking a lot out of a lot of young guys.” While he was referring to the Mets’ beleaguered offense, his words could apply to Harvey, too.

The Mets are asking quite a lot of the 26-year-old, too. The Dark Knight rose back in spring training, and at the start of the season. Now he’s slipping a little. It doesn’t mean he can’t get back up and dominate regularly again.

But it does mean these Mets, plagued by uncertainty all over their roster, have one less sure thing.