SAN DIEGO -- At some point, it’s going to start getting late.

The Mets aren’t quite there yet. After suffering a walk-off, 3-2 loss to the Padres on Sunday afternoon at Petco Park, squandering a prime opportunity to gain ground on both San Diego and Atlanta in the National League Wild Card chase, the Mets still have five full weeks of baseball to play. Thirty-one games remain, including six against teams the Mets are directly chasing, which is more than enough time for them to make up 2 1/2 games in the standings.

Their margin for error is surely growing slimmer every day, though as designated hitter J.D. Martinez noted: “A lot of crazy stuff happens in September, and we’re still in August.”

The Mets’ latest August loss dispirited them for two primary reasons. One, it came against a Padres club that has become a favorite to lock up one of three available NL Wild Card slots. Had the Mets managed to take three of four at Petco Park in San Diego, they would have made the notion of catching the Padres in September more plausible.

Two, the Mets led for much of the afternoon thanks to solo homers from Martinez and Mark Vientos, plus a vintage performance from Jose Quintana, who took a shutout into the seventh inning and finished with his finest outing in six weeks. But when José Buttó issued a one-out walk in the eighth, manager Carlos Mendoza opted to stick with him rather than turn to well-rested closer Edwin Díaz for five outs.

Although Mendoza has spoken in recent days about a willingness to begin leaning more heavily on Díaz, he noted Sunday that asking his closer for five outs seemed like one too many. The decision backfired when Buttó served up a game-tying homer to Jurickson Profar, sending Petco Park into a frenzy.

An inning later, Díaz gave up a walk-off homer to Jackson Merrill to turn a potentially uplifting series victory into a four-game split.

“Obviously, it hurts, because we’re going up against a team that we’ve got to beat to be there,” Martinez said. “But it is what it is. We’ve just got to turn the page and get ready for this next series.”

Added Díaz: “We’re good; we’re good. It’s better to win three out of four, but we split the series against a good team, a playoff team, and I think we feel good about it.”

Considering where the Mets were early this season, they have reason to feel blessed even to be in contention as August turns to September. But just as their ugly April and May gave way to a brilliant June, the Mets’ midseason success has since melted into something more ordinary. Over their past 28 games, the Mets are two games under .500. They haven’t won more than two in a row over that stretch.

This week offered another litmus test for the Mets against a Padres team with a similar record, a similar run differential and a similarly talented roster -- “I had a lot of expectations for us,” as Quintana put it. They didn’t come away feeling particularly great or awful about the result.

“The biggest takeaway is we played a really good series,” Mendoza said. “That’s a really good team right there, and it felt like a playoff atmosphere, a playoff game.”

Next up are the Diamondbacks, last year’s NL pennant winners who have won six in a row and 16 of their last 19 to establish themselves not just as favorites to earn a Wild Card spot but to lock down home-field advantage in the Wild Card Series and potentially even challenge the Dodgers in the NL West. On paper, Arizona represents a challenge perhaps even a bit stiffer than San Diego.

It is not, as Martinez noted, the biggest series of the year. But it is a notable one for a team trying to establish itself as a bona fide contender.

“These are [games] that we have to win,” Martinez said. “But when we focus on ourselves, and we can go out there, we can control our own destiny -- I think that’s the best way, the best position to be in.

“If we go out there and win in Arizona, we [also] have another series against Atlanta later on. And if we play well, we’re going to be there. It’s just one of those things where we’ve got to take care of us.”