BALTIMORE (AP) -Eager to secure a rare winning road trip and avoid a three-game sweep, the Washington Nationals turned to a rookie making his 15th big league start.

First, John Lannan endured a two-hour rain delay before the start of the game. Then the left-hander pitched longer than ever before, helping Washington secure a 2-1 victory over the Baltimore Orioles on Sunday.

Cristian Guzman homered and Ryan Zimmerman delivered an RBI double for the Nationals, who completed their first winning road trip (4-3) of at least seven games since last June.

''It was very important because you want to be in the W column as much as you can,'' manager Manny Acta said. ''We just keep battling and winning due to our good starting rotation and scratching on defense. Hopefully our offense comes alive. Then things will be a little easier for us.''

Thanks to Lannan, the Nationals were able to win only their fourth game of the year when scoring two runs or fewer. He took a two-hit shutout into the eighth and left after allowing one run and four hits in 7 1-3 innings.

Lannan (4-4) walked one and struck out five. Of his 105 pitches, 71 were strikes.

''He threw 70 percent of his pitches for strikes. That's Greg Maddux -like on his good days,'' Acta said. ''He hit the glove all day. Also we were getting quick outs. The kid deserves all the credit.''

Lannan appeared poised for his first career complete game before running into trouble in the eighth. Then another rain delay blunted the lone bit of momentum the Orioles generated during a very long afternoon.

With the Nationals up 2-0, Adam Jones singled and took third on a pinch-hit double by Luke Scott . After Acta called for Luis Ayala from the bullpen, rain halted play for 27 minutes.

''If we could have kept going right there it might have benefited us,'' Orioles outfielder Jay Payton said.

After the tarp came off, Brian Roberts hit a sacrifice fly, but Ayala retired Melvin Mora on a fly ball to end the threat.

Orioles manager Dave Trembley wasn't about to blame the weather for the defeat.

''That's just part of the game. You have to go through it. You can't make excuses about it,'' he said. ''It was a long day for everybody, a different situation you have to play through. That's it.''

Jon Rauch entered in the ninth and gave up a two-out single to Aubrey Huff before retiring Payton to secure his 10th save.

Lannan never went beyond the seventh inning before, and although it didn't happen this time, he expects to finish what he starts before too long.

''Yeah, every time I go out there I want to go the distance,'' he said. ''Seven innings is good but I'd rather go out there and throw the whole game. That's always my goal. Hopefully, by the end of the season I'll be able to do it.''

Jeremy Guthrie (2-4) gave up one run and five hits in seven innings for the Orioles, whose four-game winning streak ended. But Baltimore went 4-1 on a homestand that began with two games against Boston.

''It would have been nice to get this one today,'' Payton said. ''We were right there and had a chance to win it.''

Guzman put the Nationals up 1-0 in the third with his fourth home run, a drive to center on a 3-1 pitch. It was the team-high ninth homer allowed by Guthrie this season.

Washington missed a chance to score in the seventh when Elijah Dukes was thrown out by Nick Markakis while trying to score on a two-out single to right by Wil Nieves .

Doubles by Felipe Lopez and Zimmerman off Chad Bradford made it 2-0 in the eighth. Bradford avoided further damage by getting Lastings Milledge to hit into an inning-ending double play with the bases loaded.

Baltimore had only three baserunners over the first seven innings. Guillermo Quiroz singled in the third, Kevin Millar walked in the fourth and Mora hit a two-out double in the sixth. None of them advanced.

Notes: Nationals RF Austin Kearns was a late scratch with elbow soreness. He was replaced by Dukes, who went 0-for-3 and is 1-for-24 this season. ... Guthrie has allowed at least one home run in seven of 10 starts this season. ... Nieves had two hits and is 15-for-39 (.385) in his last 15 games.