This was the longest day and another difficult loss in a week of crushing losses for the Mets.

The Mets scored seven runs, and on a day with Noah Syndergaard starting, that would usually be a recipe for success.

It didn’t happen.

Syndergaard was lifted for a pinch hitter and only made it through five innings, surrendering six hits and four runs in the Mets’ waste of a day and perhaps season in a 10-7 loss to the Phillies at Citi Field on Sunday.

Syndergaard and the bullpen let them down, and it was another loss the Mets could not afford in their uphill battle for the second wild card.

This was the Mets’ longest nine-inning game in their history, going 4 hours and 29 minutes, eclipsing a 4-hour, 14-minute game against Washington last Sept. 23.

The flaws are coming through at the worst time of year. Even though the Cubs lost again, the Mets could not pick up ground and lost for the second straight day. They continue to lose games with Syndergaard and Jacob deGrom on the mound, having lost seven of the last 10 games started by their aces.

“It’s not just theirs,’’ Mickey Callaway said of the losses. “You have to win almost everybody’s [starts]. You have got to start winning three out of four and so it doesn’t matter who is pitching that night. You’ve got to win.’’

That’s for sure. The Mets only have 20 games left. Their next four games will be against Arizona, one of the teams they must jump to capture the second wild card. Then they have three with the Dodgers, so time is slipping away.

The Nationals won and are three games up over the Cubs. The Diamondbacks are 1 ¹/₂ games back of the Cubs, then come the Brewers and Phillies at two games back. Those three teams have 68 losses, while the Cubs are sitting on 66 losses. The Mets are 72-70, and still four games back of the Cubs in the loss column.

That is the challenge facing the Mets. It is not getting any easier as they lose ground. They need to pick up wins nearly every day now.

Once Syndergaard was out, the Mets could not get enough from their bullpen, either, and could not get the big hit from the offense against the Phillies struggling and spent bullpen.

“Noah had just given up four runs and they had scored in three consecutive innings,’’ Callaway said of his decision to pinch hit for Syndergaard with two outs and the bases loaded in the fifth. “He was at 78 pitches and you have to try and take the lead right there.’’

Pinch-hitter Todd Frazier worked the count to 3-2, but lefty Ranger Suarez got him to swing and miss on a changeup, a big inning disappeared and soon the game did as well. Relievers Luis Avilan and Justin Wilson gave up critical home runs to Mets killer Maikel Franco and Scott Kingery.

Asked if he was surprised to be removed for a pinch hitter with two outs in the inning, Syndergaard said, “No, I get it. It’s a managerial decision. I am not much of a threat offensively, especially with the opportunity to take the lead, so I understand it.’’

“Noah had a rough three innings and then two more out of the bullpen, so five straight innings we gave up runs,’’ Callaway said. “It was a tough overall night.’’

Shutdown innings would have made Syndergaard’s life easier.

“It was tough,’’ Callaway said of Syndergaard’s performance. “He looked really good early. It looked like it was going to be a good day. He really couldn’t get the ball at the bottom of the zone and left some pitches up and couldn’t get that third out, couldn’t execute that pitch to get that third out.’’

Syndergaard knew what he was up against.

“For the most part it was a so-so outing,’’ he said.

Which is about to become a so-so season for the Mets unless they go on a run.

“It’s been crunch time the last month and a half for us,’’ Syndergaard said. “With these losses it’s going to be harder to dig ourselves out of that hole.’’

The hole gets deeper every day.