The Argentina forward netted the first - as well as the third - in his side's 3-1 win over El Tri on Sunday night.
But the header was surrounded in controversy because replays showed that Tevez was clearly offside.
Furious Mexico players saw the first-half goal being shown on big screens at Soccer City in Johannesburg, but the officials could not rule it out because Fifa have banned the use of video technology.
After the game Tevez said: "At first I thought he (referee Roberto Rosetti) was saying that it was not a goal, then I saw the signal and I started (celebrating) and I was happy.
"I know I was offside, I know it was selfish but as long as they say it was a goal it's OK for me and the team.
"The team is growing in every single game, in every game it is getting stronger and we can win and that is the important thing. We can win the World Cup."
Argentina now play Germany - who were also the beneficiaries of a controversial refereeing decision - in the quarter finals on Saturday.