Philadelphia drew first blood when Travis Lee singled in Bobby Abreau.
The Mets tied the game in the second on Alfonzo's 14th home run of the year and took a 2-1 lead in the third when Rey Ordonez tripled and scored on a passed ball by Phillies catcher Mike Lieberthal.
Walker, who was part of that record setting day a few weeks ago when 62 home runs were hit over the majors, gave up another home run, this time to Jimmy Rollins, who hit a two-run home run to make it 3-2.
There it remained until the sixth as fomrer Met Joe Roa was pitching well. Roa ran into trouble in the sixth as he walked Ty Wigginton. Cedeno, whose season can be charitably called 'disappointing', turned on a Roa offering, and Roa went from being a possible winner to a possible loser.
Walker left after the fifth, and got the win. Jaime Cerda, Pedro Feliciano and David Weathers combined to stop the Phillies until the ninth, when Benitez came in and pulled his antics.
Notes-Roberto Alomar was the lone Met to have a multi-hit day, with 2.
-Sunday's game will be the third in this four-game series, with John Thomson (8-11, 4.65) facing Brandon Duckworth (6-8, 5.29).