The Mets began where they left off: with frustration.

The boos began just a few minutes and 26 pitches into the game.

David Peterson, as has often been the case this season, could not find the strike zone.

He walked Willy Adames to load the bases with one out in a first inning that promised to be like so many innings through this Mets spiral.

But after the jeers and after a brief mound visit ended, relief replaced the rage.

Peterson induced an inning-ending double play, which set the tone for a game and the club hopes for a season: The Mets have dug themselves a large hole and will need to begin climbing out.

Perhaps the process began when Peterson escaped one ditch and led the Mets to a 7-2 victory over the Brewers in front of 35,295 at Citi Field on Tuesday night.

Brandon Nimmo homered twice, Francisco Lindor crushed his 200th career dinger and Daniel Vogelbach added a two-run shot to power the Mets (36-43), who finally showed some life.

Peterson himself finally resembled the valuable piece he had been before this wayward season.

The lefty, who entered play with an 8.08 ERA, has been a mess — and not just at the major league level.

He was demoted in mid-May and posted a 6.00 ERA in his past five starts with Triple-A Syracuse.

But the Mets needed a starter to replace the optioned Tylor Megill, and Joey Lucchesi pitched Friday.

“We’ve seen some encouraging things with locations and the shape of the pitches,” general manager Billy Eppler said of Peterson before the Mets were encouraged by his results.

The lefty lasted six innings on a career-high 110 pitches, pitching around traffic (five hits and three walks) in his best outing of the season.

The Mets, whose rotation has lacked length all year, improved to 22-3 when their starter goes at least six innings.

Peterson’s performance and the offensive outburst gave the sinking Mets just their second win in their past seven games.

They still have dropped 16 of their past 22 and are far removed from playoff contention, but they will hope that Monday’s punchless, series-opening loss will be their rock bottom.

Before the game, Eppler offered manager Buck Showalter a vote of confidence and pinpointed the poor pitching as the biggest surprise of the chaotic first half for the most expensive team in Major League Baseball history.

Maybe Peterson heard him.

The 27-year-old consistently got the ground balls he needed: Ten of his 11 batted-ball outs came on the ground.

After his first-inning escape, Peterson allowed a two-out double to Mets-killer Joey Wiemer in the second, but induced a ground out from Andruw Monasterio to escape.

Two more reached without an out in the fourth inning, but Peterson got a ground ball from Luis Urias that Lindor turned into a double play.

With Adames on third with two outs, Peterson turned to his slider — traditionally his best pitch, but one that had abandoned him — and got Brian Anderson swinging for the inning’s third out.

Peterson’s final Houdini act came in the sixth inning with more Lindor help.

With two outs, Owen Miller singled on Peterson’s 102nd pitch. After a mound visit, Peterson remained in for an eight-pitch battle with Urias, who grounded sharply into the shortstop hole.

Lindor backhanded and leapt — in an effort that would make Derek Jeter proud — and threw out Urias just in time.

The Mets finally found a game in which they performed in (almost) every area.

Their defense was excellent.

The bullpen was solid outside of Jeff Brigham, who allowed two runs while recording two outs in the eighth.

And the offense offered plenty.

The Mets did not get their first hit off Julio Teheran until the fourth inning, but their first might have represented a breakthrough.

Nimmo led off the frame with a homer to right, and Lindor followed two batters later with a second solo shot.

Nimmo crushed his second blast of the day an inning later, a two-run knock that was his 10th of the season, and the Mets were rolling.

They exploded for three more runs in the sixth, when Tommy Pham’s two-out double scored Pete Alonso, and Vogelbach followed by smoking a homer to left-center.

“I believe in the talent of this team,” Eppler said before the talent finally took over.