As the Mets head into the All-Star break looking at three days off, it seems fair to ask: Can they take more time off?

Because there are no signs that what was a long, miserable and disappointing first half isn’t going to get worse in the second half.

Even though a win Sunday over the Red Sox almost certainly wouldn’t have fixed what ails them, it would have given the Mets some positive vibes, albeit temporarily.

But then a routine double-play ball that could have ended the game was hit to Francisco Lindor, and the typically sure-handed shortstop booted it to extend the inning.

A pair of walks and a bloop hit given up by Devin Williams allowed the Red Sox to tie the game, and a run in the 10th gave Boston a 3-2 win, its ninth in a row.

“I didn’t finish the play,” Lindor said of his crucial miscue. “It’s unacceptable. It’s not up to the standard I have or the organization’s standard. I’ve got to be better.”

That could have also summed up the first half, as the Mets fell to 40-57.

Only the Rockies have a worse record in the National League.

They open the second half Thursday in Philadelphia and it’s hard to imagine they could sink much lower.

“It hasn’t been fun,’’ Williams said of his first season in Queens. “There’s not a lot of celebrating going on in this clubhouse right now. We’ll take a couple days off, show up and try to do it again.”

That strategy hasn’t worked this season, one that started with lofty expectations and a rich payroll.

The home sweep at the hands of the Red Sox ended with Brooks Raley allowing the free runner to score on a sacrifice fly in the top of the 10th and the Mets unable to push a run across in the bottom of the inning.

It helped waste a brilliant outing from rookie left-hander Zach Thornton, who tossed seven shutout innings in his third major league start and a scoreless eighth from Luke Weaver.

The Mets lineup got a run in the bottom of the first when A.J. Ewing doubled and scored on Lindor’s two-bagger, and Lindor added another run with a homer in the sixth.

Those key hits were overshadowed by his mistake in the ninth in a season filled with uncharacteristic errors by Lindor.

“It comes down to we’ve got to be better,’’ said Lindor, who added of the first half: “It wasn’t good. It’s not to the standard we have here. It’s definitely not what we expected.”

Lindor and interim manager Andy Green lamented the team’s lack of execution, not only late in Sunday’s game, but throughout the season.

On Sunday, Boston’s Ceddanne Rafaela was on first in the ninth and Williams induced a grounder from Romy González right at Lindor.

Williams then walked Caleb Durbin to load the bases for Andruw Monasterio, who walked to force in a run.

Jarren Duran then blooped a single to right to tie the game before Boston went ahead in the 10th.

“He’s been great his entire career and I have a ton of confidence he’ll be great in the second half,’’ Green said of Lindor.

But their issues run up and down the roster.

“This was a tough first half in many respects,’’ Green said. “We have to take a level of ownership of it ourselves. Every single person on this team has a level of responsibility to flip the script going into the second half.”

Green insisted the Mets have “too much talent in the room to be in this spot” and was confident better execution would get them out of it.

“We’re capable,’’ Lindor said. “We’ve got some work to do.”