The co-hosts had been involved in seven matches which either alone, or jointly, opened previous tournaments, but had won none of them.
They put that right at the eighth attempt, however, as goals from Julian Quinones and Fulham's Raul Jimenez in either half gave them a victorious start against a South African side that finished with nine men.
Cesar Montes's dismissal in stoppage time took some of the shine off an otherwise upbeat afternoon for local fans.
They were a goal up inside 10 minutes when Sphephelo Sithole was caught in possession on the edge of his box by Erik Lira and the ball fell to Quinones, who drove a low shot through the legs of Ronwen Williams to give Mexico a dream start in the ninth minute.
Quinones came close to adding his second with seven minutes of the half remaining, hitting the base of a post from a Brian Gutierrez lay-off that had Williams beaten.
Sithole's miserable afternoon was complete when he was red-carded for bringing down Gutierrez just outside the box early in the second period, but it took until midway through the half for Mexico to kill off the contest.
Roberto Alvarado stood the ball up to the far post from the right and Jimenez headed in from close range.
South Africa created few chances throughout the match one of which came in the second half when Thabang Matuludi managed to get his shot away only to direct it goalkeeper Raul Rangel.Â
South Africa substitute Themba Zwane was sent off after a VAR review for appearing to strike Alvarado in the face late on as the pair tangled, on a day which firmly belonged to the host nation.
Brazilian referee Wilton Sampaio produced one more red, sending off Montes in stoppage time for a challenge on Khuliso Mudau.
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