For four innings Tuesday night against the Mets, Trevor Cahill made Braves pitching coaching Roger McDowell look like some sort of sinkerball whisperer, capable of turning around even the most troubled practitioners of the pitch.

But after retiring 12 of the first 14 batters and allowing one hit through four innings, Cahill was undone in the fifth by a leadoff walk, several well-struck ground-ball singles, and a costly error by second baseman Phil Gosselin. The streaking Mets scored four runs in the inning and rolled to a series-opening 7-1 win against the Braves at Citi Field.

The Mets have a nine-game winning streak and the best record (11-3) in the National League, and they matched their best 14-game start in franchise history in 1986. Cameron Maybin’s seventh-inning home run was the only damage done against Mets left-hander Jonathon Niese, who gave up four hits and four walks in 6 2/3 innings.

Cahill made progress since his dreadful Braves debut last week, but the husky pitcher still gave up five hits, four runs (three earned) and one walk. He fell to 0-2 with a 9.95 ERA in two starts for the Braves and 0-6 with a 9.09 ERA in eight starts since late August.

“I thought he did a nice job,” said manager Fredi Gonzalez, whose Braves lost for just the second time in seven road games. “His job is to have the other team put the ball in play, put the ball in play on the ground. And he did that. Couple of balls got through the infield. We don’t make a play behind him on the double-play ball and, well, that inning just kind of unravels on him. But I was pleased that, I think other than a couple of hits, the others were balls through the infield, ground balls. So that’s encouraging.

“I thought it was an improvement from the start before, and now he goes back out in four or five days and builds on that.”

Cahill gave up five hits, four runs and three walks in just 2 1/3 innings in an April 14 loss to the Marlins in his season debut. Tuesday’s game marked the fifth time he lasted four or fewer innings in that stretch during his past eight starts, a fact that made it tough for him to draw any satisfaction from incremental progress.

“Not really,” he said. “You go out there every time to put up a quality start. It was a little bit better than last time, but at the same time you like to at least get through six, and I feel like the first four I definitely had the pitch count and I was thinking I could go past that. Kind of just let things unravel in the fifth.”

The only Mets to reach against him through four innings were Eric Campbell on a two-out single in the second inning and Michael Cuddyer on a two-out error by Chris Johnson in the fourth, a tough call considering the difficulty of the play.

The same could not be said for the error by Gosselin in the fifth.

After Campbell led off the inning with a walk, catcher Kevin Plawlecki singled in his major league debut and Wilmer Flores singled to load the bases with none out. Cahill fell behind 3-0 in the count against Niese before inducing a grounder to second base on a 3-1 pitch. It looked like the Braves would give up a run but get a double play.

But Gosselin dropped the grounder, allowing a run to score and keeping the bases loaded with none out.

“No excuses,” said Gosselin, who made his third start of the season and second start at second base. “Trevor made a very good pitch there, should have been a double play. I just didn’t make the play.

“I think I’m going to make that play every time it’s hit to me. Unfortunately it didn’t happen today. I think I just tried to throw it before I caught it, just tried to be too quick. It’s a play I’m confident I’m going to make, it just didn’t happen tonight.”

The Braves had a majors-low one error in 12 games before Tuesday.

“That’s a routine play,” Gonzalez said, “and I’m sure Goose is going to go back and not sleep real good, because he makes that play, shoot, almost every time. Maybe he hadn’t been out there in a while and got a little jumpy.”

Gosselin’s error helped open the floodgates on Cahill, who gave up a two-run single to the next batter, Curtis Granderson, and another run-scoring single to Juan Lagares to push the lead to 4-0 and bring out manager Fredi Gonzalez to make a pitching change.

Cahill said he should have done a better job minimizing the damage better after the Gosselin error.

“That stuff (errors) is going to happen,” he said. “It’s our job to pick him up and get out of it, minimize as much as I can. It was tough that I wasn’t able to do that.”

Cahill said for some reason he got out of his rhythm when the Mets got some baserunners on and he had to pitch out of the stretch.

“Because I felt like I was in control the whole game when I was using my windup a lot,” he said. “Then they got a couple of people on, couple of hits, and I was out of the stretch. It just felt like my command after that went away.”

Other than the pitch to Maybin, the Braves didn’t make Niese or the rest of the Mets pay for any mistakes. He walked the next two batters after Maybin’s two-out homer, but reliever Alex Torres struck out Freddie Freeman looking to end the inning. The Braves were hitless in five at-bats with runners in scoring position.

“You’ve got to give (Niese) a little bit of credit,” Gonzalez said. “We had him on the ropes a few times, but we just couldn’t punch it through.”

Meanwhile, Cahill continues trying to get back to at least something resembling the pitcher he was a couple of seasons ago, before the former Oakland All-Star’s ERA ballooned from consecutive sub-4.00 seasons with Arizona to 5.61 in his 3-12 season in 2014.

In 15 starts since the All-Star break, Cahill is 2-8 with a 5.95 ERA and only five quality starts. The Diamondbacks traded the right-hander to the Braves in the final week of spring training for minor league outfielder Josh Elander. Arizona sent $6.5 million to the Braves cover more than half of his $12 million salary, and the Braves also got a draft pick (75th overall selection) in the deal.

Through the season’s first half-month, the Braves’ top three starters and main bullpen contributors have looked solid, but the back end of the rotation has not with Cahill and the well-traveled lefty Eric Stults, who takes a 6.30 ERA into his third start Wednesday.