Bryce Harper gets congratulations on his 10th-inning single from Nats first base coach Trent Jewett. (Jim McIsaac/GETTY IMAGES)

Bryce Harper, even at age 19, has become such an ingrained part of the Washington Nationals’ season that you forget how often he still encounters something new. Monday night, he played in this city for the first time. He introduced himself with a booming home run, and later the game provided Harper with a stage befitting the town’s scope.

Harper came to the plate in the 10th inning, the score tied, the bases loaded, the sky spitting rain on Citi Field. His missile of a single off New York Mets reliever Pedro Beato put the Nationals ahead and unlocked a stirring conclusion to their 8-2 victory. The Nationals, after going hitless for a span of 24 batters at one point, scored six runs in the final inning to open a seven-game trip with a win. Combined with the Atlanta Braves’ loss, the Nationals extended their lead in the National League East to 41 / 2 games.

Washington nearly spoiled another tremendous start from Jordan Zimmermann, even after Harper’s first homer in nearly a month. In the 10th, though, they left no doubt. Ryan Zimmerman, announced as the National League player of the week Monday afternoon, followed Harper’s decisive single with a three-run double. Michael Morse supplied the final salvo, a two-run homer some 415 feet to right-center field.

“We’re a confident team,” Zimmerman said. “We know if we can hang around and give ourselves a chance, that’s all we need.”

When Zimmermann starts, they always have a chance. Zimmermann allowed one run over six innings on four hits and no walks, striking out six. He has pitched at least six innings in 20 of his starts this season, and he lowered his season ERA to 2.31.

Zimmermann is not only consistent. He is dominant, and he is fighting his way, perhaps, into the conversation for best starter not only on the Nationals’ staff, but also in the entire National League. He has allowed one or zero runs in six consecutive starts, punching up a 0.95 ERA over that span.

“You always want to carry it over to the next start, and I have a pretty good streak going right now,” Zimmermann said. “Everything’s been working, so hopefully it continues.”

But it would not have mattered if not for the final inning. The Nationals did not record a hit from the final out of the first inning until Adam LaRoche singled with one out in the ninth. Danny Espinosa erased him one batter later with a 4-6-3 double play.

Roger Bernadina, who entered the game 16 for his last 31, led off the 10th with a line-drive single to left off left-hander Tim Byrdak. After Sandy Leon could not get down a sacrifice bunt, he swung and chopped the ball back to Byrdak.

Byrdak spun and fired to shortstop Ruben Tejada to start a double play. But as Bernadina slid in to second, Tejada dropped the ball, and with no outs the Nationals had two men on base. Mark DeRosa’s failed sacrifice bunt brought Steve Lombardozzi to the plate, and he ripped a single to center. Up came Harper. The crowd hurled boos at him as he stepped into the box.

“Don’t roll over and turn it into a double play,” Harper said. “That was the only thing I was thinking up there. I was trying to get some backspin on something and just get it to the outfield, score the guy on third. In that situation, that’s all you try to do.”

Beato started him with a 93-mph fastball, which Harper watched for strike one. Beato fired a curveball, and Harper bashed it into right field. Zimmerman and Morse followed to put the game on ice.

Harper’s first at-bat in the Big Apple came after Lombardozzi led off with a single off Chris Young’s glove. The crowd greeted Harper with a smattering of boos. Young worked the count to 3-2, pumping nothing but fastballs at 83 and 84 mph. Young threw another low and inside, but neither low enough nor far enough inside.

Harper crushed it. The ball rocketed off Harper’s bat and screamed into the gray sky. The only question was how far over the fence it would travel. The drive landed over the bullpens in right field, about 420 feet from home plate. Harper trotted around the bases for the first time since June 28, when he clubbed a homer in Colorado, a span of 81 at-bats.

The Nationals led 2-0, and they threatened for more when LaRoche walked and Espinosa ripped a single through the right side. They squandered the rally when Bernadina popped up, but given Young’s arsenal it seemed as though they would have chances all night. Instead, the 6-foot-10 Young plowed through the lineup. He retired 19 of the next 21 batters he faced and did allow another hit until he left the game after seven innings.

“His ball actually jumps out,” Morse said. “It plays like 91-92. He’s so big, he’s halfway down the mound before the ball comes out. He’s good. He established a high strike zone early and he was also getting the low strike.”

After their initial outburst, the Nationals did not run and hide from the Mets. They had to hold a slim lead, and in Zimmermann, they had the right man for the job.

David Wright snapped Zimmermann’s scoreless streak at 20 innings in the fourth, when he ripped a two-out homer to left field, slicing the Nationals’ lead to 2-1. Otherwise, Zimmermann mixed in sliders and curveballs with his 95-mph fastball, throwing them all for strikes, and kept the Mets flailing.

Zimmermann plowed through six innings in just 89 pitches. In the seventh, Leon drew a two-out walk with the pitcher’s spot coming up behind him. In a 2-1 game, Nationals Manager Davey Johnson sent Tyler Moore to the plate. Even if Zimmermann’s spot hadn’t come up, Johnson had already made up his mind to pull Zimmermann and conserve him.

“There was no question in my mind,” Johnson said. “He’s had a pretty heavy workload and it was one of those nights where it was rainy and kind of, the footing wasn’t real great. There was no sense in me pushing him.”

With Zimmermann out of the game, Johnson turned to Drew Storen for only one batter. He retired Wright on a long flyout to center and, he said, felt better than at any point since his April elbow surgery. But Mike Gonzalez gave up a homer on the first pitch he threw, a line drive off the left field foul pole by Ike Davis.

The Mets had tied the score. The Nationals never wavered. They knew if they hung around, there would be a chance.