Pete Alonso of the Mets reacts after grounding out to...

Pete Alonso of the Mets reacts after grounding out to shortstop in the sixth inning against the Nationals at Citi Field on Saturday. Credit: Getty Images/Mike Stobe

PITTSBURGH — Remember the Mets’ absurdly eventful and ultimately successful game in Philadelphia a few Sundays ago? When they got by with a couple of pitchers making their major-league debuts, Mark Canha had two huge homers and one extravagant bat flip, and last pitch came more than five hours after first pitch? A highlight among highlights in their remarkable season?

The Mets have had an awfully difficult time scoring since then, a trend that worsened over the weekend.

“We’ve all seen it,” manager Buck Showalter said Sunday afternoon after his team dropped a series to the Nationals and got shut down in consecutive games by starting pitchers who qualify as, by most objective measures, bad.

So maybe their rainout Monday against the Pirates, setting up a split-admission doubleheader at 12:35 p.m. and 6:35 p.m. Wednesday, was a good thing — for the hitters at least.

In a dozen contests the past two weeks, the Mets have averaged three runs per game, looking a lot more like the losing team from last season (3.9 runs per game) than the productive version of themselves this season (4.8 before this slump).

That is a small sample size, to be sure, but one that has mattered.

Their NL East lead over second-place Atlanta, which was idle Monday before starting a three-city West Coast trip, has decreased from four games to one in that stretch. This is the Mets’ slimmest advantage since July 23.

To extend a baseball cliche, in the ebbs and flows of a season, this is like a sneaky wave that was bigger than you expected, knocking you down and maybe sweeping your sunglasses out to sea. You’re not exactly in danger, but you’re less comfortable than you wanted.

“We’re still taking good at-bats,” Jeff McNeil said. “I know we’re struggling to score some runs right now, but credit to some of the pitchers as well.”

That is easy for McNeil to say. He has been among the Mets’ more productive hitters of late, hitting .310 (albeit with only a .690 OPS). Brandon Nimmo, batting .283 with an OPS of .810, has been more than fine, too. Starling Marte (.256 average, .784 OPS) and Canha (.243, .777) also are not among the chief offenders.

But look at the middle of the lineup and you’ll find the problem. Here are the lines of the usual Nos. 3-5 hitters over the past 12 games:

*  Francisco Lindor: 7-for-43 (.163), .280 OBP, .186 slugging percentage

*  Pete Alonso: 10-for-45 (.222), .286, .356, two homers

*  Daniel Vogelbach: 2-for-21 (.095), .269, .238

*  Darin Ruf: 1-for-16 (.063), .111, .063

Lindor has one extra-base hit, a double. Alonso hasn’t been “Pete-like,” as Showalter put it last month. And Vogelbach and Ruf, platoon designated hitters who combine to create effectively one hitter, have been particularly ineffective. The Mets’ total of 10 home runs in that span ranks 20th in the majors.

The Mets will have another chance against a poor-pitching team in three games against the Pirates beginning Tuesday. They’ll face Mitch Keller (4.43 ERA), Bryse Wilson (6.12) and Johan Oviedo (2.86, but almost exclusively in relief).

Washington’s Patrick Corbin (6.28 ERA) and Erick Fedde (5.08) combined to hold the Mets to two runs in 13 innings Saturday and Sunday.

Asked if he attributed the Mets’ futility to good pitching or their own failures, Showalter deviated from his usual answer of crediting the opposing team by acknowledging “probably more the latter.”

“I’m always going to give credit to the major-league pitchers,” he said, “but also, we just haven’t scored runs.”

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