Nationals third baseman Ryan Zimmerman, although holding the ball in his right hand while reaching with his glove hand, manages to put the tag on Seattle’s Ichiro Suzuki during a rundown in the sixth inning. (Toni L. Sandys/The Washington Post)

Among the current roster of Washington Nationals, the players making this city aware that competent baseball is not some abstract, imagined thing, John Lannan has seen more losses than all but one. He arrived from the minors in 2007, and everyone from that team except franchise cornerstone Ryan Zimmerman has left. He has stayed, and mostly, he’s lost.

Lannan, then, understood the significance of his latest stellar performance Wednesday night beyond its result, a 2-1 Nationals victory over the Seattle Mariners at Nationals Park. By winning 10 out of 11 games, the Nationals have surged to an even 37-37 for the season. Elsewhere, a .500 record would hardly warrant mention. But the last time the Nationals were .500 at this point in the season or later was Oct. 2, 2005, the final day of their inaugural season.

“I knew today was a big game,” Lannan said. “You kind of felt it. It’s a good place to be right now. I’ve never been on a team that’s been this far into the season and been at .500. I like it, but it’s time to kind of move past that and set new goals and start going above it.”

In another corner of the Nationals’ clubhouse, the .500 record wasn’t treated like a milestone. Zimmerman, who’s endured all but six months of the Nationals’ history, was asked what .500 meant. “Nothing,” he said. “If we continue to play good, then it will mean more at the end of the season. A ton of teams are .500 in June.”

But, Zimmerman allowed, “the past two weeks matter.” On May 30, barely three weeks ago, the Nationals reached their nadir at 22-31. They have won 15 games since — six by scoring precisely two runs, one after falling behind by six runs and another after trailing by four in the ninth.

“Baseball’s been fun again,” reliever Sean Burnett said. “We knew what we were capable of, but we had to get back to .500 before we could really see how good we were.”

Said second baseman Danny Espinosa: “I think people are going to pay more attention to us. Coming back from where we were, people probably just thought, ‘The Nationals this year, they’re going to flop.’ This team’s not like that. We’re not going to accept losing. It’s obvious losing hasn’t been accepted.”

Before a crowd of 21,367, the Nationals built their latest win on pitching. Lannan allowed one run in 52 / 3 innings on only three hits and, for the first time this season, did not walk a batter. After Lannan’s abrupt exit, which came after 89 pitches, four Nationals relievers cobbled together the final 10 outs of the game without allowing a run. Espinosa provided the brunt of the offense, driving in the Nationals’ first run and scoring the second.

The win started with Lannan, who despite being 26 is the second-longest tenured Nationals player. Before the season, Lannan scrawled “AA” underneath the brim of his cap, a constant reminder of the darkest moment of his career. He knows the date off the top of his head: June 21, 2010, when the Nationals sent him to Class AA Harrisburg, where he relearned how to pitch for six weeks.

The lesson has stuck with him. Lannan has allowed two earned runs or less in eight of nine starts, and in his last six starts he has a 1.15 ERA. He lowered his season ERA to 3.40. Five of the last six times Lannan has taken the mound, the Nationals have won.

Wednesday, Lannan retired the first 11 batters he faced and allowed five balls out of the infield all night, but he still needed ample help from the bullpen. Henry Rodriguez recorded three outs and handed the ball to Burnett with two outs in the seventh.

The Mariners summoned pinch hitter Jack Cust. Burnett induced a weak grounder to Espinosa at second with his first pitch, but Espinosa bobbled the transfer, putting men on first and second with two outs. Up came Ichiro Suzuki, an aging hitter but still a magician with a bat. Burnett worked the count to 1-2.

A single would tie the game. This season Ichiro has missed 9.2 percent of the times he has swung, the 10th-lowest rate in the majors. He averages one strikeout every 13.54 plate appearances, which makes him the third-toughest major league hitter to strike out.

Burnett threw him another sinker, this one almost at Suzuki’s back foot. Suzuki shuffled his feet as he swung and missed.

“That was the last thing I was trying to do, to tell you the truth,” Burnett said. “I was just trying to get another groundball. That wasn’t Plan A.”

The Nationals still clung to the lead they took in the fourth inning, when Espinosa singled with one out and then went to third on a wild pitch and an errant throw from catcher Miguel Olivo. With two outs, Jerry Hairston rolled a groundball into the hole on the left side of the infield. Brendan Ryan ranged to his right and made a leaping throw across the diamond, unable to beat Hairston. Espinosa scored the final run of the game.

In the first, Espinosa poked an RBI single to center, raising his average with runners in scoring position this season .340 and giving him his team-leading 45th RBI.

“I like the pressure,” Espinosa said. “Runners on base, that’s the time to really lock in. You’ve got a job to do.”

With two outs in the final inning, the crowd stood, clapped and screamed. Drew Storen froze Chone Figgins for his second strikeout and a 1-2-3 inning, his 18th save, The Nationals lined up and shook hands. It is summer, and they have won as many games as they’ve lost. It has been a long time since they could say that.

“People doubt our ability, and they have for the last couple years,” Lannan said. “And we have to be able to prove them wrong. We’re not done doing that. We’ve struggled, but it’s a new organization. It’s a great feeling.”