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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.