Chivas USA broke a six-game losing streak against Major League Soccer opponents. The Union is winless in three of its past four games.
Gavin scored his second goal of the season by intercepting Cristian Arrieta's clearance and firing a low 23-yard shot inside the right post.
Danny Mwanga gave the Union a 1-0 lead in the 21st minute with a diagonal 7-yard shot inside the right post over prone Chivas USA goalkeeper Zach Thornton.
But Thornton kept Philadelphia from regaining the lead in the 65th minute, when he slid 15 yards from the goal to make a point-blank save on Fred's shot.
Chivas USA's Jonathan Bornstein played his first game since returning from United States team duty at the World Cup.
(Copyright 2010 Philadelphia Union. Reprinted by permission)
