There was a time, not that long ago, when people thought Jon Niese might be the ace of the Mets’ rotation this season.

That was before Matt Harvey started drawing comparisons to every former great right-handed pitcher.

But Harvey, as the Mets have learned, can’t pitch every day, and while they wait to see if he can follow up his near-perfect performance in his last start when he takes the mound today, the Mets watched another subpar outing by Niese in an 11-2 loss to the Pirates at Citi Field.

The left-hander was smacked around for eight runs, matching his career-worst, in just 4 1/3 innings.

“It’s frustrating,” Niese said after falling to 2-4. “I know we need guys to go deep into games and I didn’t get it done.”

After starting the season 2-0, Niese is winless in his last five starts and Mets fans are clamoring even more for Harvey outings, as well as the arrival of Zack Wheeler.

Wheeler was scheduled to make another start with Triple-A Las Vegas last night and his potential impending promotion to the majors has drawn the attention of manager Terry Collins.

“I just talked to Wally [Backman, Las Vegas manager] at length,” Collins said of a Friday conversation. “I’ll read the report tomorrow. There’s a couple of guys out there to see him from the organization. I’ll call them and get another viewpoint. ‘How’d he look? How was his demeanor? How’d he go about things?’ ... I just want to see how he handles things.”

The Mets remain cautious with Wheeler, but he couldn’t be much worse than Niese or his teammates were yesterday in a game delayed by rain for 47 minutes in the middle of the ninth.

On top of Niese’s struggles, the offense was overmatched by Francisco Liriano, who was making his first start for the Pirates after breaking his non-throwing arm by slamming a wall in his home on Christmas.

Liriano struck out nine in 5 1/3 innings and had Mets hitters second-guessing their approach at the plate. The team has emphasized working the count, but it hasn’t resulted in more runs.