The referee's calls weren't convincing; in fact, he made some important mistakes. From the beginning, he made some doubtful decisions, especially in Mexico's favor. I also saw a permissive Chandía, more so than usual with him. He should have booked Pinto, and in the 2nd half, he correctly booked Verón after a very hard foul against Guardado. Apart from that and other little mistakes, he was OK (i.e. when booking Torrado or Marquez).
The score was 2 - 0 when Tevez took the ball, entered the area, was blocked by a Mexican defender, and fell down immediately. Chandía whistled and conceded a penalty, which I'm sure it was not... This is football, not basketball. The Mexican only protected the ball, and didn't mean to bring down the Argentinian (in fact, he didn't).
During a large part of the match, Chandía's t-shirt looked "empty". He had lost his FIFA badge, that had been stuck to one of his t-shirt's pockets. Maybe Chandía thought he was going to be demoted by FIFA? Take it easy, Carlos ... you have a lot to improve on, but you're still a top international referee. No doubts!