John Lannan had experienced most every slice of the Washington Nationals’ history, but Saturday night, tinged with desperation for his teammates, felt fresh and new for him. “I’ve never been on a first-place team,” Lannan said. “I’ve never been where it really meant something.”

Their most wrenching defeat the night before and a letdown loss in the afternoon had brought the Nationals to the brink of second place, the Atlanta Braves’ breath on the back of their necks. They had lost Bryce Harper after a foul ball bruised his ankle. As the Nationals reached their most anxious moment of their halcyon present, they turned to a part of their recent past.

Lannan came up from the minors and delivered seven dazzling innings when the Nationals needed them most. After 36 hours in which nothing went right, the Nationals salvaged a split of Saturday’s doubleheader at Nationals Park. After losing, 4-0, in Game 1, they edged the Braves, 5-2, in the nightcap and kept their lead in the National League East over the Braves at 2½ games.

“Most of the guys in this locker room felt like this was a must-win tonight,” said closer Tyler Clippard, who notched his 16th save. “We needed to get one. If they took three from us right away, it would have been a pretty big blow. John stepped up in a huge way.”

The Nationals have a chance Sunday, in the series finale, to stretch their lead back to 3½ games, right where it stood when the Braves came to town Friday. Their blown nine-run lead Friday night and a shutout loss at the hands of Ben Sheets on Saturday afternoon led to momentary panic. But Lannan hung tough after a ragged beginning and the Nationals cobbled together enough offense, capped by Roger Bernadina’s game-winning RBI single in the seventh inning, his fifth hit of the day after he came off the bench to replace Harper in center field.

The night ended with cheers from the sellout crowd. Harper came off the bench to an ovation in the eighth inning and rolled a single through the left side — then stole second base and scored on Danny Espinosa’s single, swollen left ankle and all.

Afterward, the Nationals optioned Lannan down to Class AAA Syracuse. He planned to fly back Sunday morning, back to cramped clubhouses and miniscule crowds, to a bleak stadium and sunflower shells on bus floors.

“I’ve been through a lot with these guys,” Lannan said. “I do feel a part of it. The game goes on, whether I’m here or not. I know that they’re thinking about me and I’m thinking about them.”

Music blared in the Nationals’ clubhouse and Lannan accepted congratulations, a far different vibe than after the team’s loss in Game 1. Sheets, making only his second start in two years, fooled the Nationals for six scoreless innings. They killed their own rallies with three double plays. Relievers Henry Rodriguez and Ryan Mattheus allowed three runs in two innings. They wasted Edwin Jackson’s gritty, seven-inning, nine-strikeout start. Their lead shrunk to 1½ games.

“It’s a frustrating game but we’re still in first place,” first baseman Adam LaRoche said between games. “Things could be worse.”

They put their fragile lot in the hands of Lannan, their opening day starter in 2009 and 2010, a starter who posted a 3.70 ERA in 2011 and had thrown more than 700 innings in the previous four years. “He’s too solid to be down there,” one teammate said.

But an overcrowded rotation left Lannan making $5 million in the minors. He requested a trade on the eve of opening day, but the Nationals held on to him, knowing they would need a capable starter when they shut Stephen Strasburg down for the season. At Syracuse, Lannan went 6-9 with a 4.89 ERA.

“The whole situation, it’s a business,” Lannan said. “As much as you love the game, there’s other stuff that comes along with it. As things are unfolding, I’m really excited to help this team out. This game really doesn’t owe you anything, but it can take something away. You’ve just got to be grateful for the opportunity to play this great game.”

Saturday, the doubleheader necessitated an extra starter, and the Nationals chose Lannan. His first major league inning of 2012 unfolded like a bad dream. The Braves smacked three hits and drew two walks. Chipper Jones’s RBI double and Freddie Freeman’s ensuing single but Lannan in a 2-0 hole.

Lannan calmed his nerves and brought his sinker back down to hitters’ knees. He escaped the second after a leadoff double. The Braves put two runners on base in the third, and he squirmed out of that jam. After that Lannan pitched not like a spare part, but a top-of-the-rotation left-hander – “as close to unhittable as you can get,” Johnson said.

Lannan fooled the Braves with his sinker and curveball, hitting corners and never giving them pitches they could smash. He held the Braves scoreless for the final six innings of his start and retired 13 of the last 14 batters he faced. Of his final 67 pitches, 43 were strikes. He allowed only five hits and two walks in seven innings. He gave the Nationals confidence in what he can do once Strasburg’s season ends.

“He deserves to be here,” Clippard said. “When he gets here, he’s going to contribute in a big way down the stretch. We all understand that.”

The Nationals needed to score for Lannan to secure his win. Espinosa snapped a 15-inning scoreless streak when he singled and scored, after a sacrifice bunt from Lannan, on Randall Delgado’s wild pitch.

One inning later, the Nationals loaded the bases with no outs. Adam LaRoche’s strikeout brought up Ian Desmond. He had earlier told Johnson that he aggravated his sore oblique muscle. But with the bases loaded, he told him, “You ain’t hitting for me.”

Desmond bounced a groundball to first base, slow enough to score Bernadina and tie the score as Freeman touched the bag. Desmond is “iffy” to play Sunday, Johnson said.

Sandy Leon led off the eighth with a hard groundball that bounced off first base. He moved to second when Mark DeRosa laid down a sacrifice bunt. Bernadina rolled a single through the right side against relieved Cristhian Martinez. Leon slid home with the go-ahead run.

Lannan had his win. As the Nationals poured out of the dugout, Johnson squeezed Lannan’s shoulders from behind and said, “Love you, man.” Lannan smiled wide and lined up to shake hands, on a first-place team and back where he belonged, if only for a day.

“That,” Lannan said, “was kind of cool.”

Staff writer James Wagner contributed to this report.