WASHINGTON -- Tanner Roark began the season pitching as a both a starter and reliever for Triple-A Syracuse.
He is now ending the year as one of the hottest starters for the Washington Nationals, who still have a pulse in the National League wild-card race.
Roark pitched seven shutout innings, and the Nationals added three runs in the eighth to break open a pitchers' duel and beat the Atlanta Braves 4-0 Tuesday night to sweep a split doubleheader and keep their playoff hopes alive.
Washington rallied to win the first game 6-5.
"I am not giving in to anyone, no matter who it is," said Roark, a product of the University of Illinois who improved to 7-0 and lowered his ERA to 1.08 in his third big-league start. Roark won his last six decisions for Syracuse, where he was 9-3 in 33 games (11 starts).
"He is throwing strikes down in the zone," Washington first baseman Adam LaRoche said. "One of the best performances I have seen all year."
The Nationals play the Braves for the last time Wednesday, then begin a four-game home series Thursday against Miami.
"After the Marlins, our schedule gets pretty tough," Washington manager Davey Johnson said.
Washington entered the night game 4 1/2 games back of the Cincinnati Reds for the second National League wild card. The doubleheader sweep also means that the first-place Braves (89-62) can't clinch the East division title against second-place Washington (81-70), the defending champs.
The Nationals were 0-6 at home against the Braves prior to winning twice Tuesday.
"Just a big day for us," said LaRoche, whose team led 1-0 going into the eighth inning of the nightcap. "They have been hard on us all year."
In the second game, Steve Lombardozzi hit an RBI single in the second inning.
Ryan Zimmerman crushed a solo homer, his 25th of the year, in the eighth to make it 2-0. Zimmerman has 10 homers in his last 15 games. Ian Desmond added an RBI double in the eighth to make it 3-0 against reliever Jordan Walden, and LaRoche contributed an RBI single to account for the final margin.
Freddy Garcia (1-2) allowed just one run in seven innings but was the hard-luck loser.
"He gave us every opportunity to win the ballgame," Atlanta manager Fredi Gonzalez said. "He was efficient with his pitches. You feel in a one-run ballgame anything can happen."
In the first game, the Nationals scored three runs in the bottom of the ninth inning to beat the Braves and All-Star closer Craig Kimbrel. The loss ended a streak of 37 straight saves converted by Kimbrel (3-3). The winning pitcher for Washington was another rookie, lefty Ian Krol (2-1).
In the late game, Roark, in his 12th appearance, allowed just two singles and no runs in seven innings.
"I feel like last year was a mental turnaround," said Roark, a 25th-round pick of the Texas Rangers in 2008. "I am keeping the ball low and keeping hitters off balance."
Craig Stammen came on to pitch a scoreless eighth, fanning Jordan Schafer for the final out with Elliot Johnson on second in a 1-0 game.
Washington closer Rafael Soriano pitched the ninth with a 4-0 lead in a non-save situation. He allowed two singles to open the inning but got a double-play line drive off the bat of Evan Gattis before he retired Gerald Laird on a grounder to end the game.
NOTES: The scheduled starters for the series finale Wednesday are Atlanta LHP Alex Wood (3-3, 3.45) against Washington RHP Ross Ohlendorf (4-0, 3.15) ... The Braves still hold a 12-6 lead in the season series. ... Washington's Wilson Ramos did not play Tuesday night after he made 24 starts in a row, the most of any major league catcher this year ... Nationals CF Denard Span hit a single in the fifth inning of the nightcap to extend his hitting streak to 28 games, the longest in the big leagues this year.