BALTIMORE (AP) The reason why the Washington Nationals are in first place in the NL East can be summed up in one word: pitching.
Edwin Jackson hammered home that point against the Baltimore Orioles on Saturday night, taking a one-hitter into the seventh inning to provide Washington with a 3-1 victory.
Adam LaRoche homered for the Nationals, who made the most of eight hits in improving to 10-7 in interleague play and 2-3 against Baltimore.
Jackson (4-4) gave up one run, four hits and a walk in 6 1-3 innings. He retired the first 12 batters he faced and permitted only one runner past first base through six innings.
Jackson appeared dominant, but it was actually a struggle.
''It was kind of a funny game because Edwin didn't feel too good when he started the game,'' Nationals manager Davey Johnson said.
Said Jackson: ''I wasn't sick. It was just one of those days you don't have blow-away stuff. You just have to go out and pitch. That's pretty much what it was from the time I started throwing in the pen, I knew what kind of day it was going to be.''
Four pitchers in Washington's starting rotation - Jackson, Stephen Strasburg, Gio Gonzalez and Jordan Zimmermann - have an ERA under 3.00.
''It's unbelievable,'' Johnson said. ''It just shows you how good they've been going. I'm impressed, and I'm not easily impressed.''
Washington hasn't scored in double figures this season and owns a team batting average of .238, but these guys sure can throw the baseball - as evidenced by their major-league leading 2.96 ERA.
''That's a good team, and it starts with their starting pitching,'' Orioles manager Buck Showalter said. ''And their bullpen's doing well, too.''
Such was the case Saturday night.
After Adam Jones ruined Jackson's shutout bid by leading off the seventh with a home run, the right-hander retired Matt Wieters on a deep fly before giving up successive singles.
Former Oriole Michael Gonzalez came in and got pinch-hitter Ronny Paulino to line into an inning-ending double play.
Sean Burnett worked the eighth, and Tyler Clippard got three straight outs for his 12th save in 13 tries.
Baltimore has lost four of five, scoring only six runs in that span. The Orioles were blanked twice by the Mets and needed Jones' team-high 19th homer to avoid a shutout in this one.
''You're not going to throw up a lot of runs every night, but New York had some great pitching against us, and these guys, that's why they're in first place,'' Baltimore's Mark Reynolds said. ''They've got good arms. It's tough to get a rally going against a guy like Edwin.''
Orioles starter Wei-Yin Chen (7-3) allowed three runs, two earned, and six hits in five innings. He bloodied his fingernail on a comebacker in the fourth inning, but did not blame that on his shaky performance.
''Physically, mentally and mechanically, I felt really great, but I got in some trouble after two strikes,'' Chen said through an interpreter. ''I cannot finish out.''
The Taiwan native won his three previous starts, over Boston, Pittsburgh and Atlanta. He is 0-2 with a 7.71 ERA in his two outings against Washington and 7-1 in his other 12 starts.
The game attracted 46,298 fans, the fifth sellout at Camden Yards this season. The first was on opening day, and the Phillies and Nationals each drew two packed houses.
Washington went up 2-0 in the second inning. With runners at second and third and two outs, Orioles third baseman Wilson Betemit ranged to his left to grab a grounder by Xavier Nady, then bounced a throw to first that eluded Reynolds. Nady received credit for an RBI single, and the other run came home on the throwing error.
LaRoche led off the fourth with his team-leading 13th homer, a towering fly that dropped over the center-field wall. Eleven of his last 16 hits have been for extra bases.
Baltimore's first runner came when Jones reached on an error by third baseman Ryan Zimmerman leading off the fifth. He took third on a one-out single by Wilson Betemit, and after a walk loaded the bases with two outs, Jackson retired Steve Pearce on a popup.
NOTES: Jackson is 6-1 lifetime against Baltimore, 4-0 with a 1.02 ERA over the last four seasons. ... The Orioles released 49-year-old LHP Jamie Moyer at his request. Moyer pitched in three games for Triple-A Norfolk after signing a minor league contract on June 6. ... The Orioles and Nationals wrap up the series, as well as interleague play, on Sunday. Jake Arrieta (2-5 with a 6.85 ERA at home), starts for Baltimore. Ross Detwiler (4-3) goes for Washington. ... Baltimore's Chris Davis went 0 for 4 and is hitless in his last 28 at-bats. ... Chen has allowed nine homers this season, seven of them solo shots. ... Johnson said Zimmerman might need a shot in his ailing right shoulder.