PATRAS, Greece (AP) - Three-time Olympic medalist Juan Luis Maren of Cuba beat Ion Gaimer of Moldova 11-0 Thursday in the 1383/4-pound category in the Greco-Roman World Wrestling Championships.     On the first day of elimination rounds, Olympic bronze medalist Akaki Chachua of Georgia beat Jurij Kohl of Germany to also advance at that weight.     Lazaro Rivas, who won silver for Cuba at the Sydney Games (news - web sites), beat Florin Gavrila of Romania 12-0 at 119 pounds.     Petru Sudureac of Romania, a silver medalist at the 1995 world championships, beat Jason Loukides of the United States 6-0 at 2133/4 pounds - one of two easy victories for Sudureac. Marek Svec, a silver medalist at the 1998 worlds, also won twice at 2133/4.     Rulon Gardner, the American who stunned three-time Olympic gold medalist Alexander Karelin of Russia at the Sydney Games, will compete at 286 pounds on Friday.     The championships end Sunday.