Haren pitched two innings, allowing the one run on two hits and struck out three batters.
"It felt good, especially as I was going along. It was kind of a circus to start," Haren said. "The Marlins really came out aggressive. ... I was a little out of sorts in the beginning. I fell behind guys. It's not my game to be [behind] 1-0 or 3-0. As the game started going, I was throwing more first-pitch strikes and getting better looks."
The Marlins scored their second run against reliever Tanner Roark in the sixth inning, when Solano scored on a single by Coghlan. Roark allowed three more runs in the following frame. Derek Dietrich had an RBI double, while Ed Lucas had a two-run single.
The Marlins' pitchers proved to be too much for the Nationals, who struck out 10 times in the game. Steve Lombardozzi, Danny Espinosa and Tyler Moore collected the only hits of the game for the Nationals.
"It's a boring game when we get only three hits. That's a boring game to me," manager Davey Johnson said.
Marlins right-hander Nathan Eovaldi was solid, pitching two shutout innings while striking out three batters. The only time the Marlins reached base against Eovaldi occurred in the first inning, when Denard Span led off with a walk before being thrown out trying to steal second base.
"I don't know how hard he was throwing," Marlins manager Mike Redmond said about Eovaldi. "They don't have a radar gun here. Usually you can tell by the reactions of the hitters. There were not a lot of comfortable swings in there. That's usually a good sign."
The Nationals managed to score in the bottom of the eighth inning. With the bases loaded, one out and left-hander Braulio Lara on the mound, Carlos Rivero hit a sacrifice fly, scoring Matt Skole.
Up next: The Nationals play the Mets for the third time on Thursday evening at Space Coast Stadium. The two clubs have split the first two games. Right-hander Stephen Strasburg will make his second start of the spring. In his first outing, he lasted two innings and allowed two runs on three hits against the Mets in Port. St. Lucie.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.