Cesar Ojeda, the candidate from Lopez Obrador's Party of the Democratic Revolution, trailed Institutional Revolutionary Party candidate Andres Granier by 12 percentage points, according to an exit poll by GEA-ISA consulting firm.
Exit polls for television networks put the margin of Ojeda's loss in Tabasco, where Lopez Obrador was once an Indian welfare worker, at 11 to 16 percentage points.
The apparent defeat was a personal blow to Lopez Obrador after he campaigned heavily on behalf of Ojeda in the tropical state of about 2 million people.
Lopez Obrador lost the July presidential race by a whisker to conservative Felipe Calderon. After the vote, he alleged fraud and brought central Mexico City to a standstill with protests, alarming many with strong rhetoric against his rivals.
Leading polls for months ahead of the July election, Lopez Obrador was heralded by the left as the next in a wave of Latin American presidents critical of Washington.
Lopez Obrador won a majority of votes in Tabasco in July but Sunday's poor showing for his party suggests voters may be turned off by the post-election protests and fraud accusations.
"I didn't like the ongoing protests. That's not right. Someone else won and it should be left at that, but (Lopez Obrador) keeps being stubborn," said Adriana Landeron, an office worker who said she backed the leftist in the presidential election but would not vote for him again.
Before polls closed on Sunday, the two candidates accused each other's supporters of trying to interfere with voters in isolated incidents.
Since the demonstrations in Mexico City wound up, Lopez Obrador has declared his own parallel government and promised more protests against Fox and President-elect Calderon, but his presence on the political stage is dwindling.
Granier lured support from the left in Tabasco by promising economic help for the elderly, single mothers and the handicapped -- the kind of handouts that made Lopez Obrador popular as Mexico City mayor.
Lopez Obrador himself lost a Tabasco governor's election widely seen as rigged in 1994, and staged mass protests afterward.
Copyright Reuters, 2006
