The Mets’ Brandon Nimmo, right, celebrates with Amed Rosario after Rosario legged out an infield hit in the ninth to give New York a walk-off 6-5 win over the Nationals. (Kathy Willens/Associated Press)

It happened again, this one stinging perhaps more than the others, and all the Washington Nationals could do was watch as their bullpen let another game slip away.

The steps toward that were incremental and painful. Two home runs, a few questionable decisions and, finally, a bang-bang play at first that sealed the Nationals’ 6-5 loss to the New York Mets at Citi Field on Tuesday.

Reliever Kyle Barraclough had the ball at the end, with runners on second and third and two outs, with a chance to save the Nationals from another collapse, and he got the grounder he needed to escape the ninth inning unscathed. But Amed Rosario is fast — one of the faster players in the league — and he legged out an infield single ahead of shortstop Trea Turner’s throw, leading his teammates onto the field in celebration and the Nationals into their clubhouse, chewing on another missed opportunity.

Their relievers blew a two-run lead in the seventh and a one-run lead in the eighth, and in the ninth they allowed the Mets to take the first two of this four-game series. The Nationals dropped to 19-29 and, if there was even a sliver of silver lining by night’s end, it was that the division-leading Philadelphia Phillies had a ninth-inning collapse of their own, keeping Washington from falling 10 games back in the National League East.

It is not yet Memorial Day. But what began as a rough start is now extending to the first third of the season. The Nationals, with a payroll of more than $200 million, are at risk of remaining this version of themselves.

“Mostly the seventh, eighth innings start happening or when those runs start coming in we, I mean, you definitely see a drop,” Nationals catcher Yan Gomes said. “We were still tied and you kind of saw a drop in our . . . ”

Gomes didn’t finish. He didn’t have to.

Nationals Manager Dave Martinez considered challenging the final play, checking with his video team to see if it was worth it, and quickly decided it wasn’t. But way before that, before another night began to close in, his team had a chance to win because of starter Erick Fedde and timely offense. Fedde, in his first start of the year, gave up one run in five innings . The Nationals built their first lead with a second-inning home run from Juan Soto and their second one with a two-run blast from Brian Dozier in the seventh.

Then their bullpen buckled and the game spiraled.

Wander Suero was the first reliever into the game and kept the Mets quiet with a one-two-three sixth. But Martinez pushed him into a second inning, as he had three times this season, and Suero gave up a single, walked another hitter and yielded a three-run homer to J.D. Davis. Suero entered throwing his curveball less than 10 percent of the time, according to FanGraphs, but he had two strikeouts with it in the game. So Gomes called for it against Davis, who has crushed breaking pitches this season, and that decision backfired on Suero’s 25th and final pitch.

“We were trying to expand the zone with it,” Gomes said. “And just when you leave pitches up to good hitters, they’re going to do some damage to it.”

Next came Tony Sipp to finish the seventh, Matt Grace to get the first out of the eighth and, with the Nationals ahead by one, Tanner Rainey in a huge spot. The 26-year-old joined the Nationals this weekend, from the Class AAA Fresno Grizzlies, and debuted in Monday’s loss. But he was sharp, mixing his high-90s fastball and biting slider, so Martinez gave him a chance against the meat of the Mets’ order.

That decision backfired, too. Pete Alonso, New York’s star rookie first baseman, lifted a 1-2 fastball way over the left field wall. Martinez thought it looked foul from the dugout so the umpires reviewed the play, but replay confirmed that the ball hooked inside the pole. Rainey was then left in to finish the eighth and, surprisingly, came out for the ninth of a 5-5 game with Barraclough and Sean Doolittle available.

“I liked Rainey a lot in that situation,” Martinez said. “He’s throwing the ball really well.”

Martinez considered using Doolittle but wanted to keep him ready for a potential save situation. He felt Rainey could stay effective, even as he labored through a second frame. By the time he threw his 33rd pitch, he had walked two and handed the game to Barraclough with one out. The right-hander got one grounder that was a fielder’s choice, leaving runners on the corners before a defensive indifference. Then he induced a chopper to Turner that nearly kept the Nationals from burning themselves once again.

Instead it was the punctuation mark of a blown game.

“It’s frustrating. It really is,” Martinez said. “The guys are battling, but we’ve got to start finishing games.”

Washington, 10 games below .500 for the first time under Martinez, is just two nights into a 10-game stretch against the Mets, the Miami Marlins and the Atlanta Braves. It was always going to be an important part of the schedule, all games against NL East opponents. But it has become critical.

The disappointing start could still be righted with a sharp turnaround in the next week.

Or, if this continues, it could dissolve into something worse.