Rio de Janeiro (AFP) - Brazil's President Dilma Rousseff fell ill at the end of a tense and at times bitter televised debate Thursday with challenger Aecio Neves.

Rousseff and Social Democrat Neves traded accusations for an hour and a half, after which she began to complain of feeling light-headed as she left the rostrum.

"My blood pressure dropped, let's start again," Rousseff said, as reporters ushered her to a chair and gave her a drink of water.

"I felt a bit light woozy. Sorry about that -- just one of those things," said the 66-year-old.

Just as the candidates had in their previous verbal bout on Tuesday, Rousseff and Neves, the scion of a political dynasty, accused each other of lying, misrepresentation and nepotism as they sought to impress undecided voters.

Latest opinion polls have the pair locked in a virtual tie ahead of the October 26 run-off vote.

Rousseff topped the first-round poll on October 5, with Neves claiming second place.

Rousseff, representing the Workers Party (PT) scored eight percent more votes but polls taken since the first round have business favorite Neves leading by a whisker, as they vie to lead the world's seventh largest economy and Latin America's largest country.

On Tuesday, Rousseff attacked her opponent over his two terms as governor of the southeast state of Minas Gerais.

The tone was strident again on Thursday as each candidate ripped into each other. Neves repeatedly accused his rival of "lying" only for her to retort: "You, sir, are the one who is lying."

Rousseff once again accused Neves of nepotism, given various close relatives held political office in Minas Gerais state during his governorship, a charge that he rejects.

Neves, for his part, attacked Rousseff over a kickbacks scandal at state oil giant Petrobras which a former director of the firm alleges benefited dozens of politicians, mainly from the Workers Party and its allies.

Rousseff said she ordered an investigation into the alleged graft and pointed to various corruption scandals involving Neves' Social Democrats.