Acapulco, Mexico ? Mexico’s largest left-wing party won an important victory Sunday in the Pacific coast state of Guerrero, according to initial results, in one of three gubernatorial elections that could preview next year’s national presidential campaign.

Zeferino Torreblanca of the Democratic Revolution Party had a 56 to 41 percent lead over Hector Astudillo of the Institutional Revolutionary Party, or PRI, with 76 of the vote counted. Final official results were due Wednesday.

Voters wearing bathing suits and plastic sandals filed through open-air polling places along Acapulco’s posh Costera Boulevard Sunday and in the hillside slums where many tourism industry workers live.

Guerrilla-style attacks that killed three police officers in Acapulco on Saturday and a police strike in Cancun added to worries about security for the gubernatorial elections, but no violence was reported.

The network polls also showed Democratic Revolution holding onto Baja California Sur, where the resorts of Los Cabos are located, while the PRI apparently kept control of Quintana Roo, where the resort town of Cancun is the largest city.

The Democratic Revolution Party, which finished third in the last two presidential races, was counting on a strong showing to prove it is a strong national challenger.

The PRI, which currently holds the governorship of Guerrero, was hoping the three states would pull it still further out of the crisis caused by its loss of the 2000 presidential election, ending 71 years in power.

The most bitter battleground was Guerrero, a state that lures millions of tourists a year to beaches in Acapulco and Zihuatanejo — but whose mountains also hold some of the most impoverished, violent and isolated villages in Mexico.

Each party has accused the other of trying to intimidate or buy voters and Democratic Revolution complained state electoral authorities had authorized pro-PRI companies to conduct exit polls and quick counts.

The tension grew Saturday when unidentified gunmen with automatic weapons killed three policemen and a 15-year-old bystander in the Acapulco area during three separate attacks — one of them just a few blocks from the city’s famed beach front.

Democratic Revolution’s campaign coordinator, Julio Ortega, virtually accused the PRI of murder, saying the attack was part of the party’s campaign to intimidate voters.

Victor Manuel Silva, the national PRI’s delegate to the state, blamed the city’s Democratic Revolution administration of failure to halt the violence that had killed its own police officers.

In Quintana Roo state on Mexico’s other coast, election security was complicated by a strike by some 200 police officers and by a shutdown of gasoline stations in Cancun, which has about half the state’s population.

The PRI’s Felix Gonzalez, a former Cozumel mayor, was facing Democratic Revolution’s Ignacio Garcia Zalvidea, who squabbled with state officials as a populist Green Party mayor of Cancun. Addy Joaquin Coldwell, sister of a former PRI governor, represented President Vicente Fox’s National Action Party.