But Mexico aside, most working people struggle (when they do), not to implement some ideological doctrine (e.g. "communism," "socialism," or "neoliberalism"), but to get their very basic needs met. Leftists, if they want to lead actual working people, have to proceed on the basis of this fact. Otherwise, they are not serious about becoming a political instrument of the workers.
I know for a fact that there are committed communists, socialists, etc. ("leftists") supporting López Obrador in Mexico -- just as there are supporting Peña Nieto. (As far as I know, no leftist supported the PAN candidate.) Yes Virginia, there are serious leftists working through the PRI structures and they have significant clout, organization, and popular support.
The tragedy of the left in Mexico (as in Greece, etc.) is that it is bitterly divided over strategy and tactics (some of these divisions reflect deeper geo- and socio-economic differences inherent to the diverse Mexican working class as it has evolved historically, and resolving them will be an involved process). So, under some circumstances, very unfortunately but almost "inevitably," the various wings of the left will clash frontally. Time and circumstances, and their own enlightenment, will determine how they may build some workable unity, because (I believe) such unity is indispensable.
So, again, Peña Nieto does not necessarily represent a return to "neoliberalism" or Washington consensus policies or whathaveyou in Mexico. In fact, I will guess (very tentatively, on the grounds of my recent observations while in Mexico) that he (if he manages to prevail, which is not yet a done deal) will have to shift to the "left" in many of his policies, not only to undercut the opposition movement around López Obrador and broader political conditions, but also as a result of organic pressures within the PRI.