Steven Matz pitched his gluteus maximus off Friday night, escaping jam after jam until the 10th hit he allowed to the Rockies got past a diving Wilmer Flores for the go-ahead run in the sixth inning.

With the way the Mets’ offense is trending — down — giving up even two runs was too many for Matz. He was the hard-luck losing pitcher as the Mets dropped their third straight, falling to the Rockies, 6-1, before 40,035 at Citi Field.

Yoenis Cespedes returned to the lineup after not starting Thursday because of his strained right quadriceps. He went 0-for-4 and popped up with the tying runs on base in the eighth, part of the Mets’ 0-for-8 showing with runners in scoring position.

Manager Terry Collins called a team meeting after the game. His message: lighten up.

“When you have a meeting, something’s wrong,” he said. “So I don’t like to have meetings. I just walked in and said, ‘Guys, we’ve got to lighten it up here. Tell ’em to turn the damn music up. Lighten the atmosphere around here.’ We’ve got to have joy coming to the ballpark . . . This is where we work, and the more fun we have, the easier it is to do your job. We’ve just got to quit worrying about all the bad things and start thinking about some of the good things and get ourselves ready for tomorrow night.”

Matz (8-7), who is pitching through a bone spur in his left elbow, allowed at least one hit in each of his six innings and five in his last two. Until the sixth, though, all the Rockies had to show for it was a run in the first on a two-out RBI double by Carlos Gonzales (four RBIs).

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The Mets tied it on James Loney’s leadoff homer off Tyler Chatwood (10-6) in the second.

From there, Matz did his best to walk the tightrope. Charlie Blackmon led off the third with a double and stole third before Matz walked D.J. LeMahieu. But Matz got Nolan Arenado to pop to third and struck out Gonzalez and Trevor Story.

In the fifth, Blackmon and LeMahieu singled to open the inning. Arenado hit a soft liner to first that Loney turned into a double play when he tagged the sliding LeMahieu at first. Matz then struck out Gonzalez.

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The Mets, meanwhile, had no hits between Neil Walker’s single in the second and Loney’s one-out single in the sixth. By then, the Rockies had the lead.

Story led off the sixth with a single and moved to third on Mark Reynolds’ double. With one out, Collins declined to walk No. 8 hitter Nick Hundley to load the bases and force Rockies manager Walt Weiss to hit for Chatwood. Instead, he opted to bring the infield in, which cost the Mets when Hundley sent a grounder off the glove of a diving Flores for a 2-1 lead.

Collins said he told Matz: “I know it’s hard, but tonight you don’t have your ‘A’ game. I would think it’s got to be fun to be a pitcher and go out there without your best stuff and battle really hard against a very good offensive team and look up coming out in the sixth inning and it’s 2-1. You’ve got to be pretty happy with that.”

Reynolds made it 3-1 when he homered to left off Erik Goeddel in the eighth. Pinch hitter Alejandro De Aza and Curtis Granderson began the bottom of the inning with singles, but Travis d’Arnaud, Cespedes and Loney were quickly retired. All three swung at the first pitch.

In the ninth, Collins ordered an intentional walk to Arenado to get to Gonzalez, and the Rockies’ cleanup hitter hit a three-run homer off Antonio Bastardo.