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The nationwide poll showed 40.7 percent of voters backed Humala while 40.5 percent supported Fujimori, with 18.7 percent of respondents still undecided or saying they would not vote for either.
Both candidates are courting moderate voters, who political analysts say will decide the election.
Peru's stock index gained 10.88 percent last week after three other polls also said Fujimori, who has a graduate business degree from Columbia University in New York, had gained to a virtual tie.