Mexico's old rulers claim presidential election victory

(Reuters) - Mexico's old rulers claimed victory in a presidential election on Sunday, ending 12 years in opposition after a campaign dominated by a sputtering economy and rampant drug violence.

After pledging to restore order and ramp up economic growth, Enrique Pena Nieto of the Institutional Revolutionary Party (PRI) had a clear lead over his rivals in exit polls and a "quick count" conducted by electoral authorities.

Although his main rival said it was too early to concede defeat, the 45-year-old Pena Nieto delivered a late-night victory speech to cheering supporters, and a senior electoral official said the PRI candidate's lead was "irreversible".

"Mexicans have given our party another chance. We are going to honor it with results," a visibly moved Pena Nieto told followers packed inside the PRI headquarters in Mexico City.

Jubilant supporters waved banners sporting caricatures of their candidate and his trademark quiff, and confetti in the red, green and white of the Mexican flag - and the PRI's colors - rained down inside the hall.

Outgoing President Felipe Calderon co