The leftist PRD is asking Mexico's ruling conservative National Action Party to urge its supporters to cast a "tactical vote" in favor of the left's candidate for governor of the country's most-populous state.

Voters in the central state of Mexico will go to the polls July 3 to select a new governor.

The latest polls show the real contest is between leftist candidate Alejandro Encinas and the standard-bearer of the Institutional Revolutionary Party, or PRI, PRD national coordinator Hortensia Aragon said Friday in a statement.

The candidacy of the PAN's Luis Felipe Bravo Mena "has run out of steam," Aragon said.

A survey commissioned by capital daily Milenio found that 53.5 percent of likely voters back PRI hopeful Eruviel Avila, compared with 19.4 percent for Encinas and 12.9 percent for Bravo Mena. But the PRD cites unspecified "recent polls" showing around 26 percent are still undecided.

The last debate among the three candidates highlighted "the existence of two diametrically opposed social and political models," the PRD's Aragon said, insisting that while her party stands for a "genuine commitment" to ordinary Mexicans, the PRI represents corruption.

Currently governed by the PRI's Enrique Peña Nieto, Mexico state, which accounts for nearly 13 percent of all registered voters, is seen as key for the 2012 presidential elections.

"The chances to realize the much-desired alteration of parties in the state of Mexico are real," provided PAN partisans throw their votes to Encinas, Aragon said.

The PRI, which held the Mexican presidency for 71 years prior to the election in 2000 of the PAN's Vicente Fox, has never lost a gubernatorial ballot in Mexico state.

While the PAN managed to hang onto the president's office in 2006 thanks to Felipe Calderon's narrow - and disputed - victory over PRD leader Andres Manuel Lopez Obrador, the PRI did well in the 2010 legislative elections and appears poised to retake the presidency next year.