The Federal Electoral Institute in Mexico published partial results early on Monday morning, giving Enrique Pena Nieto a sizeable lead after Sunday's general election.

Nieto is the presidential candidate for the former powerhouse of Mexican politics, the Institutional Revolutionary Party (PRI), which ruled for some seven decades prior to losing power 12 years ago.

"Mexicans have given our party another chance. We are going to honor it with results," Pena Nieto told supporters in Mexico City shortly after the partial results were announced. The PRI candidate had garnered around 38 percent of the votes counted.

The electoral commission said its "quick count" was based on a representative sample from 7,600 polling booths across the country, without saying what percentage of the overall vote that constituted. The results largely concurred with television exit polls released earlier.

Leftist challenger Andres Manuel Lopez Obrador was in second place with roughly 31 percent of the vote. He said he would not concede defeat until the counting process was finished.

"The last word hasn't been spoken yet," he said.

Departing President Felipe Calderon congratulated Pena Nieto on his win. The National Action Party (PAN) incumbent said he would work with the probable new president closely during the transition period.

Calderon's PAN party colleague Josefina Vazquez Mota looked set to collect third place in the race, with partial results putting her at 26 percent of the vote. She conceded defeat in the early hours of Monday morning.

Pena Nieto has spearheaded a comeback for the long-dominant PRI, promising economic growth, a reduction in violent crime and tax and labor reforms in his election campaign. The PRI had ruled Mexico for 71 years prior to being voted out in 2000.

As well as choosing a new president, voters were electing representatives for both houses of Congress, six state governors and the Mexico City mayor in Sunday's polls.

msh/sgb (AFP, AP, dpa, Reuters)