NEW YORK -- There was speculation all week that Mets ace Jacob deGrom was going to pitch in the final game of the first half on short rest. But manager Luis Rojas decided against it and went with a bullpen game on Sunday afternoon at Citi Field. The results didn’t come out the way he wanted as the Mets fell to the Pirates, 6-5.

The Mets used six relief pitchers in the game -- including opener Aaron Loup -- and they blew a 5-0 lead. It was a game in which Trevor May and Seth Lugo, two of the team’s best relievers, were unavailable because of recent usage. Rojas refused to call the loss the worst of the season.

“All the losses are tough,” he said. “This is tough. … We had an early lead. We had a 5-0 lead. We didn’t get much going afterwards.”

New York entered the ninth with a 5-4 lead, but closer Edwin Díaz couldn’t lock down the save as he allowed a game-tying RBI single to John Nogowski. Two batters later, Wilmer Difo made it a 6-5 game with an RBI single, and the Mets were unable to rally in the bottom half.

“I came into the ninth to do my job, but I wasn’t able to do it today,” Díaz said. “... I tried to battle, keep the inning close and tried to win [the game] in the ninth.”

The Mets fell to 47-40 on the season, and they hold a 3 1/2-game lead on the second-place Phillies (44-44) in the National League East.

“We jumped on them pretty quick with five in the first,” Mets right fielder Michael Conforto said. “We weren’t able to add any on. … Some things happened. Some runs were given up during the game. We should have been able to put up a couple of more runs as the game went on.”

If the Mets are going to win the NL East, they will need major contributions from Conforto.

The game started as if the Mets were going to blow out the Pirates when they scored five runs in the first inning against right-hander Chase De Jong. Francisco Lindor gave New York a 2-0 lead with a two-run homer.

After Dominic Smith and Jeff McNeil reached base on walks, Conforto came to the plate with a .195 batting average. Conforto worked the count to 1-1 and then clobbered the ball over the right-center-field wall to give the Mets a 5-0 lead. It was Conforto’s first home run since May 1, breaking a streak of 31 games without a homer. When he’s hot, Conforto is capable of being one of the team’s top run producers.

“We’ve worked on some things, and it’s gotten me to the point where I feel more like myself,” Conforto said. “From top to bottom, we are starting to get healthy. J.D. [Davis] is coming back. It’s just going to create more and more depth, more great bats. I would expect to see the bats heat up as we get into the summer. The pitching has been solid all year. We expect the same from those guys, too.”

De Jong had a lot to do with the Mets being blanked the rest of the way, according to Pirates manager Derek Shelton. De Jong held them scoreless for four innings after the first.

“I think that starts with Chase. I mean, he goes out in the first and doesn't have it, and [then he] bounces back and gives us five strong,” Shelton said. “After he got through the third and he continued to execute, we kind of fed off that.

“And then all of a sudden, we get the two homers and it's 5-2, and we continue to grind and create opportunities. There's a lot of teams that [are behind], 5-0, last day of the first half, you're not gonna see that effort. These guys continued to get after it, and I applaud them for it."

The Mets needed their bullpen to hold Pittsburgh in check. By the sixth inning, New York’s lead was down to one run, and the Pirates mounted a threat in the eighth.

Pittsburgh had the bases loaded with one out, and it was up to Díaz to get out of the jam, as Rojas went to him for a five-out save chance. He showed why he is one of the best stoppers in the NL by striking out Michael Perez and pinch-hitter Ke’Bryan Hayes to end the threat.

But Díaz couldn’t finish the deal in the ninth. After the game, the Mets had a team meeting. Lindor reminded his teammates that they had a great first half. He told them to take the time to relax, get their minds off the game, work on parts of their game if needed and keep playing like a first-place team.

“There are no heads hanging in there,” Conforto said. “But obviously, we would have liked to get that win.”

Said Díaz: “We are in a good position right now. We are going to try to win every game. Today was a tough loss. We stay together. Right now we go home, don’t think about the loss and come to the second half strong.”