Philadelphia (8-6-10) defender Sheanon Williams was called for a handball when a pass from Robbie Rogers hit him on the left wrist as he tried to shield himself.
Mendoza's shot was initially stopped by Faryd Mondragon but the ball rolled underneath him to cross the goal line.
Emilio Renteria scored for the Crew (11-7-7) in the 37th minute with a left-footed redirect of a pass from Rogers, but the Union equalized five minutes later on their seventh corner kick, with Veljko Paunovic heading the cross from Keon Daniel that goalkeeper William Hesmer had no chance to stop.
(Copyright 2011 Philadelphia Union. Reprinted by permission)