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It was a wonderful day for Jordan Zimmermann. For six innings.

Zimmermann allowed just one hit and a walk while sailing through six innings Sunday, but ran into trouble in the seventh. Nick Markakis led off with a single and Vladimir Guerrero hit an 0-2 pitch into the left-field seats for a two-run homer.

The ill-timed breaking pitch was the difference in the Washington Nationals' 2-1 loss to the Baltimore Orioles.

Through the first six innings, Zimmermann (2-5) was nearly perfect, retiring 13 straight after allowing a second-inning walk and a double.

That 0-2 breaking ball to a notorious bad-ball hitter?

"I tried to bounce a curveball and it just hung up a little bit. He got a big barrel on it," Zimmermann said. "He's a tough hitter to pitch to. You just have to mix it up. Throw balls in the dirt, throw high and in. You just have to pretty much mix it up and hope for the best."

Guerrero's home run was just the third Zimmermann has allowed in 54 1-3 innings this season.

The Nationals scored 17 runs in the opener Friday night, then lost the final two games in the Beltway Series.

"That's too bad because we got another good pitching performance," manager Jim Riggleman said.

Zimmermann walked Luke Scott with two outs in the second and Mark Reynolds followed with a double to center. After that, the right-hander retired 13 straight before Markakis' single. He allowed four hits in 6 1-3 innings, striking out five and walking one.

Guerrero had two or more hits in each of his previous seven games — the longest such streak of his career. But he hadn't homered since April 28.

"Vladimir is a guy where there is no safe spot to pitch him," Riggleman said. "They've got that American League lineup where you're going to see four, five guys in a row come up there. You may get them out but somebody is going to pop one sooner or later. That's why you have to score some runs to have a margin for error."

Jim Johnson (3-1) got the win with a scoreless seventh. Koji Uehara worked the eighth and Kevin Gregg pitched the ninth for his eighth save in 11 chances.

Gregg walked Matt Stairs with one out, then struck out Roger Bernadina as pinch-runner Brian Bixler tried to steal. Matt Wieters threw out Bixler to end the game.

"Kevin's got great timing to the plate," Wieters said. "So normally if you make a good throw, you are going to have a pretty good chance to get him."

Chris Tillman started and pitched five innings for Baltimore, allowing a run and six hits.

The Nationals' only run came in the fourth after Jayson Werth led off with a double. Wilson Ramos walked and, with one out, Tillman hit Danny Espinosa with a pitch. With two outs, Alex Cora hit a ball off Tillman's right leg for an infield single that scored Werth.

Bernadina flied out to end the inning.

While the Orioles offered no run support for Tillman, he was fortunate to leave with only a single run against him. Washington was 1 for 8 with runners in scoring position while he was in the game.

NOTES: Riggleman was ejected in the first inning when Bernadina, the leadoff batter, was called out for making contact with the ball outside the batter's box. Bernadina had reached first on a bunt. "I didn't even have an argument. I was just irritated that the call was made," Riggleman said. "The call was right but it's a call you never see get made." ... Washington 1B Adam LaRoche was out of the lineup with a sore left shoulder. Riggleman said LaRoche would have it checked on Monday. He's in a 1-for-29 slump. ... Orioles LHP Brian Matusz, on the disabled list all season because of a strained rib cage muscle, threw 70 pitches in six innings for Double-A Bowie on Saturday. Matusz will throw again Tuesday. Manager Buck Showalter hinted that Matusz would make another rehab start before he's activated. ... Wieters' 10-game hitting streak ended.