The win pushes the Nats' National League East lead over the Braves back to 2 1/2 games, calming a groundswell of nerves after dropping the first two games of the four-game series and three straight. Earlier in the day, the Braves rode a spectacular outing from Ben Sheets to a 4-0 win.
"We played well today and got off to a good start with a two-run lead in the second game and then just stopped," said Braves third baseman Chipper Jones, who hit a pinch-hit home run in the ninth inning of Game 1.
Atlanta pounced quickly on Lannan in the first inning. With two outs, Jason Heyward walked and then scored on a double by Jones, who started at third base and went 1-for-3 in the nightcap. Jones came home when Freddie Freeman ripped a single to right, giving the Braves a 2-0 lead.
But after that first frame, Lannan retired 18 of the next 22 hitters he faced to hold the Braves at those two runs for the remainder of his outing.
"I had nothing to lose tonight, it was a win-win for me," Lannan said. "I had this opportunity to come up here and help the team win. I just went out there and had that mentality."
The Nationals managed only three hits through four innings, but their bats came alive in the fifth. A Danny Espinosa walk and Sandy Leon single put runners on first and second with one out, and Lannan came to the plate already having notched a single in the third. Lannan laid down a textbook sacrifice bunt to advance the runners to second and third. A wild pitch from Braves starter Randall Delgado scored Espinosa on the next play. Delgado earned a no-decision through six innings of two-run, six-hit ball.
With Bryce Harper held out of the nightcap's starting lineup after fouling a ball off his left ankle in the first game, Roger Bernadina stepped in at center field. Batting in Harper's No. 2 spot in the order, Bernadina was 5-for-7 on the day, including 3-for-4 in Game 2 with a run scored. In the seventh inning, he delivered one of Washington's most important hits of the year with a two-out single off Braves reliever Cristhian Martinez, scoring Leon from second base and giving the Nationals the 3-2 lead.
Harper entered the game as a pinch-hitter for reliever Sean Burnett in the eighth, knocking a single to left field, stealing second base and then scoring on Espinosa's single. Espinosa later scored on a throwing error by Braves shortstop Paul Janish.
"It's definitely big," Bernadina said. "I tried to get on base to help the team, and things turned out well for me. It's good we got the W."
In the ninth, the Nats found another source of relief when Tyler Clippard picked up his 16th save of the season. Clippard allowed only a walk to David Ross, recovering from two blown saves in his last three attempts.
"I felt like myself again, able to locate my fastball good and throw some good changeups," Clippard said. "It felt good. It felt good to get one out of the way."
Mostly, though, the night belonged to Lannan. After leading the Nats with 10 wins in 2011 and taking the mound as the Opening Day starter in both 2009 and '10, Lannan was forced into an entirely different role this season. With the team eager to give hard-throwing left-hander Ross Detwiler an expanded role, Lannan requested a trade shortly before Opening Day 2012 after it became apparent that he would not make the big league roster.
But with the team's ace, Stephen Strasburg, pitching under an innings limit this season, the Nats need another pitcher on tap once their ace is shut down, potentially in the heart of a pennant race.
"Every game means something, but right now we're in the battle for the [National League] East," Lannan said. "I just want to go out there and do my job."
Since he was activated as the 26th man on the roster, a rule allowed for doubleheaders, Lannan was optioned back down to Syracuse following the game.