PHOENIX — Last season, as the Mets raced to the National League pennant, stars emerged.

Yoenis Cespedes arrived in a midsummer trade and transformed the lineup. Matt Harvey, Jacob deGrom and Noah Syndergaard provided high-octane heat from the mound. Jeurys Familia established himself as one of the game’s best closers.

Yet, from start to finish, nobody proved more valuable than Curtis Granderson.

But a year later, with the Mets clawing to keep their postseason hopes alive, Granderson has found himself caught in the same malaise that has ensnared his teammates. His productivity across the board has dipped.

“This guy was our MVP last year,” manager Terry Collins said. “He isn’t having the same year, but we’re going to look up at the end of the year and he’s still going to have some home runs.”

That belief in a turnaround is best reflected in Tuesday’s starting lineup against the Diamondbacks. Despite a slump that has sent Granderson’s average tumbling to .226, he remains locked in the second spot, behind Jose Reyes.

Granderson had been the Mets’ leadoff man before the arrival of Reyes. It wasn’t an ideal fit, though he grew into the role, a key development because the Mets did not have any viable alternatives.

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But now that he has been moved down, Granderson said he may make a conscious effort to get more aggressive at the plate.

“Initially, I was in a position of leading off and trying to set the tone, things like that,” Granderson said. “I mixed when to be aggressive versus trying to set the tone for everybody else. There’s been pitches that I could have gone after and attacked that I could have done something with that I let go by.”

Granderson, 35, hit .259 with 26 homers and 70 RBIs last season. He posted a healthy .364 on-base percentage in the leadoff spot while becoming a stalwart in rightfield.

But this year, Granderson’s on-base percentage had slipped to .317 entering Tuesday night, partially because his walk rate has slipped from 13.3 percent last year to 10.4 percent. He has 18 homers but only 31 RBIs — a combination of batting leadoff and his struggles to hit with runners in scoring position.

Though he’s a .239 hitter with runners in scoring position in his career, Granderson was hitting just .127 in that department this season, a staggering dropoff from the .297 average he posted a year ago.

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An explanation has proved elusive.

“There’s no real reason, not 100 percent sure what it is,” he said. “I just haven’t been able to have success and get it done when I’ve needed to.”

Since July 7, Granderson is 1-for-24 with runners in scoring position and hitless in his last 15 at-bats in such situations.

“Hopefully things will change,” Granderson said. “There’s nothing else you can do. You can’t practice it. You can mentally say OK, in this round of batting practice, we’ll pretend there’s a runner on second, a runner on third. But it’s completely different depending on who the runners happen to be, who’s pitching and who’s coming into the game to face you.”

With the Mets teetering on the edge of the wild-card race, Granderson has slumped badly, hitting just .172 in his previous 22 games.

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Even with a glut of lefty hitting outfielders, a numbers game that hastened the demotion of Michael Conforto, Granderson has remained a fixture in the lineup. And it seems that Collins has no plans of dropping the struggling veteran down in the order.

“You move those guys down to the bottom of the lineup,” Collins said, “they get on base and there’s nobody in the lineup to drive them in.”