The Juventus defender rose above the Mexican defence to head home in his first international since the 2002 World Cup to save ten-man Uruguay from their fifth consecutive defeat.
Mexico, themselves needing a good result after some recent lacklustre performances, had gone ahead in the 69th minute when Pavel Pardo scored with a serving, dipping 30-metre shot.
Uruguay were reduced to ten men when substitute Richard Morales was sent off in the 80th minute for a challenge on Pardo -- just two minutes after coming on for Dario Silva.
In between, the fiery Morales was denied an equaliser when his shot was saved by Oswaldo Sanchez.
The game began slowly although Montero, who has smashed records for red cards and suspensions in Italy's Serie A, quickly made his mark as he picked up a yellow card just 28 minutes into his return.
Montero, who had announced his international retirement in 2002 but then changed his mind, steadied the nervous Uruguay defence, which had conceded 11 goals in losing their last three World Cup qualifiers.
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But the Charruas stayed in front for only three minutes before Ricardo Osorio equalised with a speculative lob which appeared to get some help from the wind as it flew over helpless Luis Barbat in the Uruguay goal.
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