Shortly after Jose Reyes re-signed with the Mets last season, Sandy Alderson was asked about the veteran’s diminished defense at shortstop. The general manager insisted that Reyes wouldn’t see time at that premium position.

More than a year later, Reyes has become entrenched at shortstop for a team that has spiraled out of contention, partly because of a porous infield defense. Alderson has long sacrificed gloves for bats, and on Tuesday night, the effect of that constant compromise was on full display.

In a 5-0 loss to the Cardinals, Michael Wacha tossed the first shutout of his career, and the Mets committed three errors to cement their reputation for butchery.

“It was a hard game for us defensive-wise right out of the gate,” Reyes said.

T.J. Rivera, a .296 hitter with no true defensive home, committed two errors. Manning third base, where his offensive production has nudged him ahead of Wilmer Flores, Rivera made an errant throw and failed to knock down a routine grounder. Both plays ended with Tommy Pham reaching base.

Then there was Reyes, who has played the majority of his games this season at shortstop because of Asdrubal Cabrera’s diminished range.

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Reyes himself is past his best days at the position. But he has been a default choice only because the Mets believe top prospect Amed Rosario needs more seasoning in the minor leagues, even though he would provide an instant defensive upgrade at short. On Tuesday, that choice proved costly.

In the second, Kolten Wong legged out an infield single on a grounder hit to Reyes. Though hardly an egregious lapse, it was a play likely made by a more accomplished fielder. But in the second, Reyes paid for a poor transfer that made him unable to turn what should have been a ground ball double play by Cardinals starter Michael Wacha.

“I should make that play 99.9 percent of the time,” Reyes said. “It’s one of those days.”

Mets righthander Rafael Montero bore the brunt of the fallout, allowing four runs in six innings though only two were earned. It took only two innings for shoddy defense to put the Mets in a 4-0 hole against Wacha, who was stingy by allowing just three hits and throwing 119 pitches.

The Mets began the day 10 1/2 games out of a playoff spot, prompting them to inform players that playing time may be shaped by the upcoming July 31 nonwaiver trade deadline. By the end of the evening, the Mets 41-50 dropped their third straight game, all during a stretch in which Alderson said a sell-off would be avoided by playing “exceedingly well.”

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“In this league, you can’t give away outs,” manager Terry Collins said.