President Barack Obama will throw the ceremonial first pitch when the Phillies open the season Monday against the Washington Nationals at Nationals Park.

Pregame ceremonies begin at 12:30 p.m., with the game scheduled to start at 1:05. Roy Halladay is scheduled to make his Phillies debut and will be opposed by the Nationals' John Lannan.

Obama's appearance will mark the 100th anniversary of the first time the president threw an Opening Day first pitch and the 48th time a president has done so in Washington. On April 14, 1910, William Howard Taft began the tradition before the Washington Senators went on to defeat the Philadelphia Athletics, 3-0, behind a one-hit, complete game shutout by Hall of Fame pitcher Walter Johnson.

Individual tickets are no longer available. The Nationals are selling 400 seats in sections 401 and 402 for $5 starting at 10 a.m. on game day at Nationals Park Main Box Office.

Due to enhanced security and an anticipated sellout, the Nationals are urging fns arrive an hour to two hours earlier than normal. Gates will open at 10 a.m.