NEW YORK -- What happens in September won’t mean much come October. But if the three-game series between the Dodgers and Mets was, indeed, a preview of the NL Championship Series, Los Angeles hopes to play a whole lot better seven weeks from now when it matters most.

Despite a strong return from Clayton Kershaw, the Dodgers’ sloppy defense, a baserunning mistake and a lack of timely hitting was ultimately too much to overcome in the 5-3 loss to the Mets on Thursday at Citi Field.

“We beat ourselves,” said Dodgers manager Dave Roberts. “I think there’s nothing, for me, more frustrating than not playing fundamental defense. And when you give teams extra outs, there’s a collateral effect. … I think that you could look at four runs they scored in the sixth and the seventh was a byproduct of, we didn’t secure the baseball. This whole trip, I don’t think we played great defensively.”

Throughout the season, the Dodgers have prided themselves on playing elite defense. It’s something they believe can be the difference in the postseason. But it was their defense that let them down on Thursday.

In the sixth, Starling Marte hit a weak grounder to where the second baseman is usually located. But with a slight shift on for the righty hitter, Gavin Lux had to race over a few steps to his left to make the play. Lux, however, took longer than he would have liked to fire off a strong throw, allowing Marte to reach with a leadoff infield single.

The Mets took advantage and scored two runs in the inning, taking a lead they wouldn’t relinquish. They added two more runs in the seventh, also because of a defensive lapse. Lux and Mookie Betts had some miscommunication in shallow right, allowing a popup from Brandon Nimmo to drop between them that extended the inning and ultimately put the game out of reach.

“That’s probably a ball I’ve got to catch,” Lux said. “I got turned around a little bit, but it’s a ball I’ve got to catch.”

Against most teams, the Dodgers can mask some defensive mistakes because they suffocate opponents with their talent. But that wasn’t the case against the Mets, who own the second-best record in the National League.

Los Angeles had plenty of chances against New York, but the club went just 4-for-20 with runners in scoring position en route to dropping two of three in the series.

In the second with the bases loaded, Chris Taylor delivered a bloop two-run single down the right-field line, but some miscommunication between third-base coach Dino Ebel and Trayce Thompson got the center fielder thrown out at the plate. Betts grounded out six pitches later, ending the threat.

Los Angeles was then able to create traffic against closer Edwin Díaz, who was summoned against the Dodgers’ heart of the order in the eighth inning. After Freddie Freeman and Will Smith reached to start the frame, Max Muncy and Justin Turner each came within a few feet of tying the game with a three-run homer.

Instead, the Dodgers settled for a long Muncy flyout and a Turner sac fly to cut the deficit to two. Díaz then blew a 102.8 mph four-seam fastball, the hardest-thrown pitch of his career, past Lux to end the scoring chance.

“They’ve got good pitching. We’ve got good pitching,” said Freeman. “It’s going to be like that if we do face them in the playoffs. … This is kind of what’s going to happen with two good teams.”

While the Dodgers will fly home frustrated with the result, the biggest key was to get Kershaw back on the mound and looking healthy. In his first start in a month, they were hoping to get four innings from Kershaw. He delivered with five, allowing just one run on one hit and three walks while striking out six.

“It was great to get back out there, obviously,” Kershaw said. “Wanted to be out there for a while. First inning was a little rough, obviously, but thankful to kind of bounce out of that and get through five at least.”

Getting Kershaw back in the rotation gives the Dodgers more insurance, especially given the sudden uncertainty surrounding Tony Gonsolin’s right forearm. The Dodgers will rely heavily on Kershaw in the postseason. But in the meantime, they’ll try to get hot again and hope to avoid a similar repeat outcome in the event they return to New York next month.

“If we do face them in the playoffs, no one is going to care what happened in the regular season, nor the scores of those games or what transpired,” Freeman said. “We just didn’t come out on top this time.”