Duterte, the tough-talking mayor of the southern city of Davao, emerged as the "clear frontrunner" in a survey which research institute Social Weather Stations (SWS) released today.
The candidate, who has promised mass killings of suspected criminals, saw his support rise from 27 per cent of respondents in March to 33 per cent in April, giving him a nine-point lead over second-placed Senator Grace Poe just two weeks before the vote.
Duterte, 71, had told laughing followers that the woman was so beautiful he wished he had been the first in line to rape her -- before she was murdered in a jail riot in his city in 1989.
SWS spokesman Leo Laroza said the apparent joke may have dented Duterte's popularity but did not stop him pulling ahead of his arrivals in the poll of 1,800 voters.
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"Mayor Duterte has been steadily gaining ground. It's a clear lead. The joke could have affected him in such a way that his score could have even been higher had it not been for that news," he told AFP.
It showed marked sympathy for his "one-issue campaign effort" against crime and illegal drugs, he added.
The survey also indicated that issues like women's rights and human rights in general were secondary for many.
"There is much to be desired about the quality of political education" in the country, Magno said.
He said Duterte also benefited from having three rivals splitting the vote. If the anti-Duterte forces were eventually to unite behind one of them, that might determine the election result, said Magno.