Ruling party conservative Felipe Calderon won Mexico's presidency on Tuesday, ending a long legal battle over vote fraud claims, but his leftist rival vowed to fight on in the streets.
Seven judges at Mexico's top electoral court unanimously ruled that the July 2 vote was fair and pro-business candidate Calderon won by about 234,000 votes out of 41 million cast.
Leftist candidate Andres Manuel Lopez Obrador rejected the decision and said he would never accept Calderon as president.
"I will not recognise anyone who parades himself as the head of the federal government without any legitimate or democratic credentials," he told supporters in Mexico City's central Zocalo square on Tuesday night.
Lopez Obrador plans to set up a parallel government and block Calderon's attempts to run the country.
His followers wept openly after Tuesday's ruling and angrily accused the judges of selling out to Mexico's rich elite.
The election split the nation of over 100 million along class lines. Leftists have since paralysed central Mexico City.
In an attempt to heal wounds, Calderon, 44, promised to give priority to Mexico's millions of poor after he takes office on December 1.
"The election is over. Now is the time for unity and agreements," he told supporters. "Only united can we defeat the real enemies: poverty, crime, unemployment and inequality."
Calderon's victory provides the United States with a key ally in Latin America, where leftist presidents critical of Washington have taken power in recent years.