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Matilde Campodonico, Associated Press
Tabare Vazquez, center right, presidential candidate for the ruling Broad Front party, embraces a follower after voting during the presidential runoff election, Sunday, Nov. 30, 2014, in Montevideo, Uruguay. Vazquez, a former president, is favored to win the runoff on the back of a strong economy.

MONTEVIDEO, Uruguay — Tabare Vazquez shook up Uruguayan politics when he became president in 2005, peacefully ending 170 years of two-party dominance. Now, as Uruguayans vote on Sunday, he's the face of continuity as he seeks to extend his left-leaning coalition's decade in power.

A series of pre-election polls gave Vazquez a roughly 10-point lead over his rival, Luis Lacalle Pou of the conservative National Party in the South American nation of 3.2 million people.

Tall and trim, the 74-year-old oncologist is almost the physical opposite of outgoing President Jose Mujica, who is short, paunchy and famously informal. But both support social programs that have improved life for the poor as well as continuing moderate economic policies.

In his first presidential campaign, Vazquez promised changes that would "shake the roots of the trees." But he governed as a relatively cautious moderate, avoiding the constitutional changes and polarization that have shaken countries such as Venezuela.

Vazquez has said he will leave in place a law to give Uruguay the world's first government-run marijuana market, though he said he would retreat if it has negative results.

Lacalle Pou is the son of another ex-president, Luis Alberto Lacalle Herrera, who governed from 1990 to 1995. A 41-year-old attorney, he has promised to improve education and public security, areas in which Mujica's government was often criticized. He has also said he would shut down the state-run marijuana market, while allowing domestic cultivation of the plant.

He's hobbled by some voters' wariness of a return to the traditional parties that ruled through most of the country's usually peaceful history, apart from a 1973-1985 military dictatorship.

"They did nothing for us. Now it is our turn, the poor. That other crowd governed for the other half, for the rich, not for the poor," said street vendor Elvio Sosa.

Son of an oil worker, Vazquez grew up in a working class neighborhood of Montevideo and went on to achieve a medical degree. He's also the former president of a professional team based in his home district of La Teja.

Vazquez continued seeing patients one day a week during his previous presidency, but said in a recent interview that he would give up medicine to focus on the presidency if elected on Sunday.

Uruguayan law forbids consecutive re-election so Vazquez had to leave office in 2010 when his five-year term ended. This year, he fell just short of a first-round victory in October, getting 48 percent of the vote against 31 percent for Lacalle Pou.