* Serra knocked Rousseff's infrastructure, health policies
* Analysts say no clear winner in debate
* New poll shows Serra 10 points behind Rousseff
(Recasts, adds details of debate, analyst comment)
By Raymond Colitt and Brian Winter
BRASILIA, Aug 5 Ruling party candidate Dilma Rousseff looked set to pull away in Brazil's presidential race on Thursday as she opened up her biggest lead yet in polls and emerged largely unscathed from the first nationally televised debate.
Rousseff was hesitant at times but displayed a clear command of statistics and policy in a polite and mostly uneventful debate with three other candidates including her main challenger, former Sao Paulo state governor Jose Serra.
A new poll out Thursday showed Rousseff with a 10 point advantage over Serra. Rousseff has benefited in recent weeks from Brazil's robust economy and the popularity of President Luiz Inacio Lula da Silva, who has campaigned actively on her behalf.
Just over six months ago, Serra had a 20 percentage-point advantage in polls. But in the TV Bandeirantes debate, Serra passed up several opportunities to hit Rousseff hard, preferring instead to make general criticisms of Brazil's poor infrastructure and health system.
"Traveling on federal highways in Brazil today is a public danger," Serra said.
Serra faces the difficult task of needing to remain the critical opposition candidate while not alienating the vast majority of Brazil's electorate who are satisfied with the economy and Lula's government.
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"(Serra) successfully targeted some of the government's weak spots but didn't score major points," said Rafael Cortez, political analyst with Tendencias consultancy in Sao Paulo.
One of the debate's key moments came early, when Serra was given the opportunity to ask Rousseff a question directly. Yet instead of asking about corruption scandals that forced several of Lula's top advisers to resign, for example, he asked Rousseff for her views on health, education and crime.
"Brazil has advanced step by step," Rousseff replied.
NO "CLEAR WINNER"
Even if Serra had scored major points, the debate's importance was arguable. It began at 10 p.m. and faced competition for viewers from a crucial soccer match. Fireworks could be heard in Sao Paulo with each goal.
Rousseff, a technocrat who has never stood for public office, faced the challenge of emerging from Lula's shadow and displaying a sometimes absent common touch.
She occasionally stumbled in her response but gave an overall solid defense of her track record in the government, citing job growth, economic stability, and poverty reduction.
"She may not be an excellent speaker but she didn't make any major mistakes. I didn't see a clear winner, an event that would change the course of the election," Cortez said. (Editing by Jackie Frank)