Polls closed under a heavy rain in the Chiapas capital, Tuxtla Gutierrez, with no reports of violence, although one election observer said irregularities were widespread. About 1,000 national and foreign observers monitored the vote.
``We've documented many irregularities: busing in voters . . . and other tactics to secure the vote" for Sabines, said Enrique Vera, of the Mexican Electoral Observation Movement.
Sabines, an ally of Andres Manuel Lopez Obrador, the PRD's presidential candidate, said his winning would help stabilize the country.
Aguilar promised to govern for all and ``leave behind the retaliation and persecutions" of the current PRD-backed administration.
Mexico's capital and the southern city of Oaxaca have been under siege by political protests for more than a month. Lopez Obrador, has called for around-the-clock protest camps to try to overturn the slight advantage Felipe Calderon of the National Action Party has in the July 2 presidential vote, citing election fraud.
In a surprise move, President Vicente Fox's National Action Party, or PAN, withdrew its candidate in Chiapas and threw its support behind Aguilar.
It was the first time National Action has formed an alliance with the PRI since Fox ended the PRI's 71-year hold on the presidency in 2000.
Some had little faith in either candidate.
``Neither one is going to make a difference in my life," said Pascuala Lopez, a Tzotzil Indian woman selling grilled corn in San Cristobal de Las Casas.
Police arrested four men for possible electoral violations, including a prominent labor leader allegedly carrying about $5,000 in cash to buy votes for the PRI.
And a recording was handed over anonymously to electoral officials of an alleged conversation between Manuel Espino, national leader for the PAN, and a local PRI official about money to buy votes.
Miguel Ballinas, a spokesman for the PAN in Chiapas, said the tape was not authentic.
Many fear a loss in Chiapas by Lopez Obrador's PRD could spark confrontations in Chiapas, the site of bloody political clashes in the past.
``Chiapas is a point of influence for other states, and for that reason we must be more aware of who we vote for, and we have to pray that everything turns out well," said Victoria Anta Carrillo, 64, among the first at the polls.
In the July 2 presidential race, PAN candidate Calderon has a slight advantage over Lopez Obrador, former Mexico City mayor. Lopez Obrador's supporters are blocking the heart of Mexico City in a protest demanding that electoral judges grant a total recount.
On Sunday in Mexico City's central plaza, Lopez Obrador, speaking to thousands of supporters, suggested electoral judges, who are among the nation's highest paid officials, were under pressure to accept bribes.
The Federal Electoral Court has until Sept. 6 to announce a president-elect or annul the election.
