But in typical Lannan fashion, he battled back and was able to get out of the inning. Matt Wieters then hit into a double play, and Robert Andino grounded out.
"It was huge getting the double play in that situation," Lannan said. "You need some kind of play like that. That really helped out. It really helped my pitch count. I made a good pitch to Wieters down and away. "
Lannan cruised until the eighth inning, when he gave up a pair of hits.
"We expect that out of him -- these type of outings every five days," manager Manny Acta. "He gives us a chance to be in the ballgame. It didn't start the way it ended. In the beginning, he was a little bit off. He had four leadoff walks in the first four innings, but he made his pitches when he had to. He had good sink to his fastball. He gave us a very solid outing."
Lannan declined to call himself the leader of Washington's rotation. All he would say was that the future is bright because of the young staff that includes Jordan Zimmermann and Craig Stammen.
"We are all learning together. We have some great coaches and great catchers who are helping us develop faster," Lannan said. "I never considered myself a leader. We all have each other's back. We all try to push each other to do better. If someone throws eight or nine innings, I want to try to do the same thing and just try to build off each other."
But Acta seems to think Lannan has established himself as the leader of the young rotation.
"I think he is [establishing himself as the ace] without a lot of hoopla or anything like that," Acta said. "I think the other kids realize that, too. He doesn't have the 96-mph fastball. He leads by example. He works very hard. He does what he has to do. So I think a lot of the other kids look at him."
Once Lannan settled down on the mound, Washington's offense took over, thanks to Adam Dunn, Willie Harris and Josh Willingham.
The Nationals were able to get to O's starter David Hernandez in the fourth inning, when Dunn hit a monster two-run homer to right. The ball landed on Eutaw Street and hit the warehouse behind Oriole Park on one bounce.
Asked if he got all of it, Dunn said, "He jammed me a little bit. Yeah, I got it pretty good. I haven't hit a homer in a while. It was a really good feeling today. When you hit them far, you tend to not feel them as much, because there is no vibration. Luckily, we got two and not one [run]."
When Dunn reached the dugout, Harris didn't even shake his hand or praise him for the job well done. Such praise wasn't needed.
"You didn't have to say anything for that," Harris said. "I just looked at him. We looked at each other. I just turned my head, and it was unbelievable."
The Nationals added a run in the sixth inning, when Anderson Hernandez singled up the middle to drive in Willingham.
An inning later, Harris hit a home run off Chris Ray, while Willingham scored in the eighth on an error by Wieters.
"It was very nice, especially the home run by Willie," Acta said. "He gave us some breathing room. He continues to play well. Willingham basically manufactured that run by himself. That was big. It proved that we needed it in the end."