Argentina set up a championship match against Brazil, which will be played Sunday in Maracaibo.
Mexico, invited along with the United States to take part in this South American regional championship, had pulled off a surprise by getting to this stage of the competition.
But while Mexico had its chances, with two shots bouncing off the goalpost, Argentina had by far the most opportunities.
After Heinze gave Argentina the lead at the half, Lionel Messi made it 2-0 in the 61st minute by sending a high floater over the head of Mexican goalkeeper Oswaldo Sanchez.
Juan Roman Riquelme added a goal on a penalty kick in the 65th minute.
Mexico will play Uruguay in the third-place game Saturday. The American team did not make it past group play.