PHOENIX -- Trevor May dropped in an 81.6 mph slider near the bottom of the zone, and then he turned and watched as the ball came off the bat of Josh Reddick. It sliced down the right-field line, and May thought it was foul.

However, first-base umpire Jordan Baker signaled fair. The Mets challenged, to no avail, as the call stood, resulting in the tying and winning runs crossing the plate in a 6-5, 10-inning loss to the D-backs at Chase Field on Tuesday night.

Shortly after the loss, May stated he still believed it was a foul ball. But Mets manager Luis Rojas knows that MLB’s replay center in New York had better views than the lone clip shown on the scoreboard in the ballpark.

“Tough to say,” Rojas said. “I’ve got to stick to what they saw. I mean, I know they have more angles than we do.”

Regardless, it marked an off-night for a bullpen that has pitched well over the first two months of the season, helping lead the Mets to a terrific May in which they went 17-9 (the third-best mark in the National League). Closer Edwin Díaz had converted each of his first nine save opportunities this season, but he couldn’t preserve a 4-3 lead in the ninth, giving up a game-tying RBI single to Josh Rojas.

Díaz prevented the D-backs from winning it in the ninth, and the Mets took a 5-4 lead in the top of the 10th on a leadoff pinch-hit RBI double by James McCann. At that point, New York went to May, who had given up two runs in two-thirds of an inning on Monday.

Seth Lugo, who was activated from the injured list ahead of Monday’s game, was available. Luis Rojas, however, said the Mets are waiting for an opportune spot for the right-hander to make his season debut. This evidently wasn’t it.

Instead, Rojas turned to May, who had been told to start throwing more sliders. He did, using the pitch for seven of his 10 offerings. But the last one resulted in the game-ending hit.

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“He just lost the command, but he’s who we went to,” Rojas said. “He’s a guy that’s been high leverage for us that we trust. The situation there after using Díaz, gets us out of the inning, and we felt that May could have helped us to close the deal there.”

On May 8, May owned a 1.46 ERA through his first 13 appearances. Things haven’t gone as well for him over the past 2 1/2 weeks, as the right-hander has given up at least one run in five of his past eight outings, posting an 8.10 ERA over that span.

May said that his pitches have felt “less than sharp” of late. He also knows that he can’t rely solely on his fastball to produce results over the course of a 162-game season, which is why he’s working on his breaking balls.

“These stretches happen pretty much once a year, and it’s trying to adjust and change your game plan based on what the guys in the box are showing you,” May said. “These guys prepare for you in a certain way, you get in patterns and then you’ve got to get out of those patterns and get back to what makes you good.”

The Mets held a 4-0 lead after five innings, and they were up by one run after starter Marcus Stroman (three runs allowed in six frames) exited. Even though New York’s bullpen gave up three runs in the final two innings, it still has a 3.59 ERA this season, which ranks fourth in the NL.

Rojas is confident that his relief corps will bounce back and that this won’t be the start of a tough June for his first-place club.

“We’ve just got to get our heads up and move forward,” Rojas said. “We have a good bullpen. They’ve done a tremendous job. They’re a big part of why we’re in this position right now.”