With Roy Halladay on the disabled list for an extended period of time, rookie Jonathan Pettibone has a golden opportunity to prove he belongs in the major leagues. After six starts, the 22-year-old has done nothing to disappoint. Pettibone will try to keep his undefeated record intact when Philadelphia visits the Washington Nationals on Saturday. Dan Haren, who has lost his last two outings, takes the ball for Washington. He is 0-3 with a 6.10 ERA in four starts versus the Phillies.

The Nationals won the opener of the three-game series 5-2 on Friday, the first time they've scored at least five runs in six games. Washington has the second-worst batting average in the major leagues at .227, but has remained above water thanks to a 3.50 ERA - seventh-best in baseball. Philadelphia is not much better at the plate (.248), but slugging first baseman Ryan Howard has raised his average 17 points to .262 after going 6-for-13 in his last three games.

TV: 7:15 p.m. ET, Fox

PITCHING MATCHUP: Phillies RH Jonathan Pettibone (3-0, 3.00 ERA) vs. Nationals RH Dan Haren (4-5, 5.54)

Pettibone has not allowed more than three runs in a start and Philadelphia has won in five of his six outings. The Placentia, Calif., native allowed two runs (one earned) in seven innings, but the Phillies bailed him out when they delivered back-to-back home runs in the ninth inning to defeat Cincinnati 3-2 on Sunday. Pettibone, who has yielded 36 hits in 36 innings, isn't overpowering with 21 strikeouts and has recorded nine of his 11 walks in his last three turns.

Haren has yielded more hits than innings pitched in four of his previous 10 major-league seasons - and finished with a losing record in three of them. He has allowed 64 in 50 1/3 innings this year. Haren has yielded nine or more hits four times in 2013, including nine in his last outing when he allowed seven runs in five innings in a 13-4 loss at San Diego on Sunday. Philadelphia's Youngs - Michael and Delmon - are hitting a combined .329 versus Haren.

WALK-OFFS

1. The Nationals' Davey Johnson, 70, and Charlie Manuel, 69, are the oldest managers in the major leagues.

2. Phillies RHP Mike Adams (back) is expected to be activated Sunday after a bullpen session Friday went well.

3. Washington RF Bryce Harper is 5-for-24 in seven games since he was injured after crashing into the wall at Dodger Stadium on May 13.

PREDICTION: Nationals 3, Phillies 2