Bryce Harper, left, congratulates Michael Morse (38) on his fourth-inning grand slam, the first for the Nats this season. (John McDonnell/THE WASHINGTON POST)

This magical Washington Nationals season has been building with each win, road trip and homestand. With each passing series, they bolster their claim to the best record in baseball and bring their playoff dreams closer to reality. And in one moment on Friday night, the excitement came spilling out.

Michael Morse clubbed his team’s first grand slam of the season, a go-ahead blast in the fourth inning against the New York Mets. Caring little that another player was up to bat, fans at Nationals Park kept cheering and applauding, drawing the long-haired and goofy hero from the dugout. He thrust his arms into the air. It wasn’t a sellout crowd, but it felt like it. Baseball was alive and well in Washington.

The Nationals dispatched the Mets, 6-4, pushing their record to 29 games over .500 and maintaining a four-game lead in the National League East. The taste of losing seasons was replaced by an energized fan base, a healthy and potent lineup and a dominating array of pitchers. The buzz could have been felt across the Anacostia River.

“It makes you a little kid again to kind of look around,” starting pitcher Ross Detwiler said of the atmosphere provided by the crowd of 34,827. “It’s one of the best feelings in the world.”

“We’re playing good baseball,” said shortstop Ian Desmond, who was activated from the disabled list before the game. “Everyone’s hustling and playing the game the right way. It was nice to see them come out. Obviously these aren’t probably the biggest games we’re playing on this homestand. But they were out supporting us tonight.”

The thought of having everyone together for Friday’s game was so mouth-watering that Nationals Manager Davey Johnson penciled out a lineup with Desmond’s name in it days in advance. Injuries had claimed, for varying stretches of the season, Morse, Desmond, Ryan Zimmerman, Adam LaRoche and Jayson Werth. But Friday, an offense that had already defiantly shed its midseason torpor was as complete as it would be this season.

Desmond failed to log a hit in four at-bats, though his timing didn’t seem terribly off after 25 games away. But the Nationals don’t depend on him to the extent they did earlier this season. He could jump back into the lineup and be boosted by the bats of Werth, Bryce Harper, Zimmerman and Morse. Those first four hitters of the lineup went a combined 7 for 15 with six RBI on Friday. Harper showed signs of potentially breaking out of his slump, hitting a single and a laser of a two-run home run.

“The whole middle of the lineup is really in a good spot, and that’s why we’ve been scoring a lot of runs,” Johnson said.

The Nationals fell behind 2-0 in the first inning as Detwiler struggled with his command. His fastballs were too high in the strike zone and he couldn’t find a good feel of his secondary pitches. There were lingering effects of the nose and stomach illness that affected his last start. It resulted in three straight base hits and two runs, then a four-pitch walk — all with two outs.

From the second inning until his exit after the sixth, it was completely different for Detwiler. His sinkers dipped and induced groundballs —13 of them in all. Detwiler’s recovery was enough to allow his teammates at the plate to erase his early errors.

Mets starter Johan Santana’s first run-through of the Nationals’ lineup was dominating. He sat down the first nine hitters in order. But this lineup would not be fooled twice.

Werth slapped a single to center field to lead off the bottom of the fourth inning, followed by singles to the same spot by Harper and Zimmerman. The bases were loaded for Morse, who could sit and wait for a fastball on either half of the plate.

With the count 1-1, Santana reared back and fired a high, outside fastball. Morse drilled it. He skipped out of the batter’s box, watching his handiwork sail into the right field seats. In 10 at-bats against the left-hander, it was Morse’s first hit.

He ran around the bases, did his trademark slap of the helmet and met the three teammates he drove in out in front of the dugout. He forcefully slapped their hands, pulled off his helmet and screamed as he ran into a crowd of high-fives in the dugout.

For the crowd, that wasn’t enough. After a walk up and down the dugout, Morse jumped onto the dugout steps and thrust his arms into the air. The crowd erupted, a tingling feeling of excitement not often see around here.

Last season, Morse carried a less potent Nationals lineup with 31 home runs. This season was short-circuited by a lat muscle strain that held him out of the first 50 games. He finally found his groove in late June, and has only gotten hotter: Over the past 10 games, he is 13 for 41 with four home runs and 11 RBI.

With Friday’s home run, Morse extended his hitting streak to 13 games. He often shied during his breakthrough 2011 season, and on Friday he wasn’t available to talk to reporters.

“The way he’s swinging the bat now, he’ll probably end up with 80 RBIs and hit his .300 again,” Johnson said. “But I’d say the last 10 days, he’s the old Michael Morse.”

The home fans cheered again an inning later as they watched Harper crush a Santana pitch into the right field seats, adding to the Nationals’ lead.

Detwiler allowed only one more run, as did reliever Craig Stammen. Drew Storen pitched a scoreless eighth inning and Tyler Clippard notched his 26th save, pitching around two walks.

And yet again, the Nationals convened in the infield for celebratory high-fives amid a chorus of applause and cheers. The excitement was real. Things are clearly different around here.