The offside call during the Mexico versus South Africa game was made correctly. The ESPN announcers were wrong. There must be two opposing players between the offensive player and the goal.
Yes, Steven Pienaar was standing in goal, but the keeper had come out to try to win the cross and so only one player remained ahead of the Mexican forward Carlos Vela.
Usually, of course, the keeper is in the goal and so if the player is even or behind just one player when the ball is played he’s onside, as the keeper is the second player. The play happened very quickly, so hats off to the linesman for making the right call in such an important moment.
Giovani dos Santos's header looked like it was going wide, so Vela had to try and chest the ball into the goal. But if Vela was not in the play, or avoided the ball, would the ball have gone in on it's own? It's hard to say.