The Fire lost the 2015 MLS season opener to the reigning champions 2-0 at the StubHub Center in Carson, California but it could have been a different result had the visitors been awarded a penalty early in the second half.
Quincy Amarikwa appeared to be brought down in the area by Robbie Rogers but the Fire striker did not provide any protest and the away team got nothing from referee Jair Marrufo which Yallop feels may have been the wrong decision.
"It's a tough place to come and play, and win, and do anything, but I just felt that moments are everything in a game: we don't get a penalty call that I felt was a penalty," said Yallop.
"I've got to look at it again but it felt like it was from where I was sitting, and then within a minute they go down the other end and score. That's football."
Jose Villarreal scored with a blasting left foot in the 65th minute after an error from Fire captain Jeff Larentowicz before 2014 MLS MVP Robbie Keane added a second in the 81st minute with a lovely volley from just inside the area.
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