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. The Long Island lefty was the hard-luck losing pitcher as the Mets dropped their third straight, 6-1, to the Rockies before 40,035 at Citi Field.

Yoenis Cespedes returned to the lineup after not starting Thursday because of his strained right quad. Last year’s trade-deadline acquisition went 0-for-4 and popped up with the tying runs on base in the eighth, part of the Mets’ 0-for-6 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,” Collins 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 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 Carlos Gonzalez’s two-out RBI double.

The Mets tied the score on James Loney’s leadoff home run off Tyler Chatwood (10-6) in the second. It was Loney’s sixth home run.

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 to keep the game tied.

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 to end the inning.

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

Story led off the top of the sixth with a single and moved to third on Mark Reynolds’ double to left. Matz, who threw six shutout innings in his last outing in Miami, got David Dahl to fly out to short left.

Collins declined to walk No. 8 hitter Nick Hundley to load the bases and force Rockies manager Walt Weiss to hit for Chatwood. Instead, Collins opted to bring the infield in, which cost the Mets when Hundley sent a grounder off the glove of a diving Flores to give the Rockies a 2-1 lead.

Matz worked out of further trouble and left after 104 pitches. He walked one and struck out five.

Collins said of Matz’s performance: “I just saw him in the lunch room and I said, “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.”

Chatwood went seven and gave up one run on three hits. He walked four and struck out four.

Reynolds gave the Rockies a 3-1 lead when he homered to left off Erik Goeddel in the eighth.

The Mets put the first two men on against reliever Jake McGee in the bottom of the eighth on singles by pinch hitter Alejandro De Aza and Curtis Granderson.

Travis d’Arnaud, elevated to the No. 2 spot, hit a broken-bat grounder on the first pitch from Scott Oberg to third for a forceout when Arenado tagged De Aza. Cespedes fouled out to first and Loney grounded to second to end the inning, both on the first pitch.

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