MONTEVIDEO Tabare Vazquez looked set to win his party's primary by a landslide on Sunday, clearing the way for him to run again to be president of Uruguay, the country he led between 2005 and 2010.
With 31 percent of votes counted, Vazquez, a doctor by profession, had received about 82 percent of the votes cast to choose the candidate for the left-wing Frente Amplio bloc, election authorities said.
Vazquez's opponent, Senator Constanza Moreira, had won 18 percent of the votes. The official count tallied with earlier exit polls.
The term of President Jose Mujica, also of Frente Amplio, ends in March 2015, with the election due to be held this October. Frente Amplio - which under Mujica has pursued radical policies such as marijuana legalization - is ahead in opinion polls with around 44 percent of support.
Traditional center party the Partido Nacional has been polling around 26 percent, while the right-wing Colorado party has been scoring around 16 percent.
Pedro Bordaberry, son of ex-dictator Juan Bordaberry, was on course to be chosen as the Colorado candidate on Sunday, while Luis Lacalle Pou, also the son of an ex-president, was ahead in the primary for the Partido Nacional, official data showed.
Vazquez pursued a center-left agenda in his first term, combining social welfare reforms with conservative economic policies. Less radical in office than ex-guerrilla Mujica, Vazquez opposed Uruguay's recent legalization of abortion.
In a speech on Sunday, he pledged to tackle high inflation, lower taxes, and give extra support to social and education programs.
Less than 40 percent of voters participated in the primaries, a historic low.