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06/23/11 9:17 PM ET

Capital gains: Nats earn sweep on walk-off

Riggleman steps down after Washington's 11th victory in 12 games

WASHINGTON -- It was a genuine old-fashioned pitcher's duel on Thursday afternoon between Jason Marquis and Seattle's Michael Pineda.

Pineda is a power pitcher, while Marquis relies on a devilish sinker to make batters beat balls into the dirt time and again. Both had everything working in this game, and nobody scored until Washington got a few good breaks in the bottom of the ninth that set up pinch-hitter Laynce Nix's sacrifice fly for a 1-0 victory before 21,161 at Nationals Park.

The win completed a three-game sweep for the Nationals (38-37), who have won 11 of their past 12 games. Eight of the wins have come by two runs or fewer; five of the victories were one-run decisions.

Normally, that would be the big news of the day. But the sudden and surprising resignation of Nationals manager Jim Riggleman minutes after the game trumped everything.

Riggleman stepped down, unhappy with his contract situation. He's been on one-year deals, wanting to talk about his option being picked up for next year, and general manager Mike Rizzo said he wasn't ready to do that yet. Riggleman said if they couldn't talk, he couldn't manage.

John McLaren will be the interim manager for this weekend's series with the White Sox in Chicago.

The players were stunned by the news. Rizzo said that when he told the players, the clubhouse went from very happy to somber immediately. But the one thing most players who would speak said was the same -- there's a game in Chicago on Friday night, and they've got to be there.

"We've been playing great baseball," said shortstop Ian Desmond. "It's a little mixed bag right now. We've got to go out and play. We've got to move forward, play as hard as we can for whatever manager's [here]."

Marquis nearly made news of his own, taking a no-hitter into the sixth inning. He didn't surrender a hit until Pineda got his first Major League hit on a bloop to center field with one out in the sixth.

The veteran right-hander turned in one of his best performances of the season. He gave up three hits in eight shutout innings, striking out four and walking three, totaling 70 strikes on 108 pitches.

"I think you have to tip your cap to Marquis a little bit," said Mariners manager Eric Wedge. "I haven't seen him in a long time, but he went out there and pitched a pretty good ballgame. He had pretty good stuff and was throwing the ball where he wanted to."

Pineda matched him, scattering four hits over seven shutout innings. He threw 97 pitches, 70 of which were strikes, and struck out nine. The Nationals threatened in the first, fourth and seventh, but Pineda emerged unscathed each time.

Jayson Werth doubled with one out in the first, moved to third on a wild pitch and tried to score on a Ryan Zimmerman fly ball to center. Franklin Gutierrez stopped that with a perfect throw home.

Washington loaded the bases with one out in the fourth but couldn't score. The Nationals also put runners on first and second with two outs in the seventh, but left them stranded.

In the ninth inning, the Nationals finally manufactured a run against right-hander Chris Ray (3-2). Michael Morse led off with a single to left field and moved to second when Danny Espinosa reached on a bunt single that just rolled under Ray's glove towards second base.

That proved to be a key play. Ivan Rodriguez tried to sacrifice, and first baseman Adam Kennedy scooped it up and gambled, throwing to third in an attempt to get pinch-runner Brian Bixler. But Bixler easily beat the throw to load the bases with none out.

Jerry Hairston hit a shot that shortstop Jack Wilson made a diving stop on and quickly threw home to force Bixler. Nix lined a bullet to left field. Mike Carp caught it, and Espinosa tried to score, even though the ball wasn't hit deep. Carp's throw was a little up the line, and Espinosa easily came across with the game-winning run.

"Big hit by Nix," Werth said. "Big sacrifice fly by Laynce to give us the ballgame. Once again, the pitching was good."

Tyler Clippard (1-0) got the victory after pitching a scoreless ninth that included two strikeouts.

The Nationals have won two consecutive games despite scoring a total of three runs to finally make it over the .500 mark.

"We won," Hairston said. "The bottom line is winning. Doesn't matter if it's 1-0 or 15-14. It doesn't matter."

Jeff Seidel is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.