MEXICO CITY — Angry and frustrated over corruption and violence, Mexican voters have delivered a tidal wave presidential election victory to leftist Andres Manuel Lopez Obrador, giving him a broad mandate to upend the political establishment and govern for the poor.

An official quick count from electoral authorities late Sunday forecasts that Lopez Obrador would win with between 53 percent and 53.8 percent of the votes, a remarkable margin not seen in the country for many years. Early Monday, with about 20 percent of the votes counted, Lopez Obrador's advantage was close to the quick count's statistical sample.

A prominent exit poll predicts his party allies are poised to score big victories in congressional races, possibly winning absolute majorities in the Senate and the Chamber of Deputies.