While Pena Nieto, 45, is the youngest of the candidates but he has struggled to gain support among university students, in part because of some missteps.
After the heckling incident earlier this month at posh private university, some of his supporters said the protesters weren't really students or had been manipulated by rival candidates. That led to about 130 of them to make a video posted on social media sites, in which they were seen holding up their student IDs and denying they had been manipulated.
The involvement of private university students in the forefront of Saturday's protests was unusual in Mexico's heavily class-conscious political sphere; the more working-class student bodies at public universities have played more of a role in the past.
Young people have had only a sporadic involvement in Mexican electoral politics the past. For example, in the failed 2006 presidential campaign of leftist Andres Manuel Lopez Obrador, older voters — many of whom benefited from the ex-mayor's pension scheme — formed the hard core of his support.