NATAL, Brazil - Oribe Peralta scored a second-half winner in a 1-0 victory over Cameroon in rain-lashed Natal in a match which once again raised questions over the standard of refereeing at the World Cup.
Miguel Herrera's Mexico side dominated throughout but went in for the half-time break feeling aggrieved after seeing what looked like two perfectly valid goals chalked off for offside.
Those decisions did little to appease a Mexican media which cried foul after seeing Group A opponents Brazil awarded a questionable penalty in a 3-1 win over Croatia on Thursday.
The possibility of yet another refereeing blunder appeared to have crossed the mind of Herrera, who said afterwards: "I told the boys before the match to keep their focus on our gameplan, whatever happens.
"Human error exists. We have to learn to put up with whatever comes our way. We didn't think about the referee when we went back to dressing room (at half-time).
"Concentration is essential and the lads did well to keep their composure."
Volker Finke, the German coach of a Cameroon side whose pre-World Cup was marred by a bitter row over bonuses, refused to use the "difficult" playing conditions as an excuse.