The victory snapped the Nationals' three-game losing streak and improved their record to 6-15.
Lannan, 23, ended up pitching seven innings and giving up five hits. It marked the second consecutive game in which Lannan had a quality outing. Last Thursday, he pitched six innings against the Mets and struck out 11 batters.
On Tuesday, it was hard to figure out who was the veteran and who was the rookie on the mound. The only time the Braves had runners in scoring position against Lannan was in the second and fourth innings, but they all came with two outs.
"It was something to watch," Nationals manager Manny Acta said. "I was telling some of my coaches, 'Sure I want to win every single night, but with the plan we have here and what we are trying to accomplish, an outing by this young man is worth three or four of those losses I have suffered all ready.'
"This is back-to-back good outings. It shows a lot about this kid. John Lannan against John Smoltz, who is chasing 3,000 strikeouts. Lannan just matched him up inning-by-inning."
What makes Lannan so special, according to Acta, is that he not afraid to face big league hitters, and he throws almost nothing but strikes.
"Regardless of the situation -- Barry Bonds, Smoltz's 3,000 -- he is very focused on hitting that mitt," Acta said. "He does it very well. When he does it, he has success up here."
Lannan was in awe of watching Smoltz reach the milestone as the veteran struck out Felipe Lopez in the third inning, but Lannan has learned to block out the situation when he is on the mound.
"I watched Smoltz since I was a little kid, so it was great to be part of it. I'm glad we got a win out of it, too," Lannan said. "You have to block it out. If it does affect you, it has to affect you positively."
Another amazing thing about Lannan is that he makes adjustments. On April 12, the Braves pounded Lannan, who gave up six runs in four innings. It was a different story on Tuesday. Lannan kept the ball down.
"If my fastball is up, then I'm going to get hurt. I have to work on locating my fastball," Lannan said. "[The last time,] I just got hit. I was leaving balls up. You have to keep the ball low against these guys. If you leave it up, you will get hurt."
The Nationals scored their lone run off Smoltz in the top of the second inning, thanks to Willie Harris, who played with Smoltz in Atlanta last year. On a full count, Harris doubled to right to drive in Lastings Milledge.
"It's good to help the team any way you can," Harris said. "I was looking for something out over the plate. I know he is a tough pitcher. He throws 3-2 curveballs. A lot of guys come right at you. He is not going to give in regardless if you are a leadoff hitter or an eighth hitter. You have to be ready. He is a competitor."
The Nationals were able to score five more runs in the ninth inning off right-hander Jorge Campillo. The biggest blow came when Ryan Zimmerman doubled off right-hander Chris Resop to drive in two runs. Both of those runs were charged to Campillo.
The Nationals' bullpen did a great job. Ray King, Luis Ayala and Jon Rauch shut Atlanta down over the final two innings. With closer Chad Cordero potentially missing time with a shoulder injury, the Nationals need the rest of the relievers to step up. Prior to Tuesday, they were not doing a good job.
"It was a good team effort from the bullpen," Acta said. "We had a tough decision to make at the end. Ayala doesn't match up well with Chipper [Jones] or lefties. And Ray King hasn't been getting the righties out, but he stepped up today. We need him to do that."
A historical moment indeed. But it was Lannan, who spoiled the night for Smoltz and the Braves.
"You've got to tip your cap," Smoltz said. "He just flat-out outpitched me."