Left-wing former army commander Ollanta Humala had a razor-thin lead over the right-wing daughter of a jailed ex-president in Peru's presidential election on Sunday, partial official results showed.
With three-quarters of ballot boxes counted, Humala had 50.087% support and lawmaker Keiko Fujimori 49.913% - a difference of only around 20,600 votes.
Election officials said the first official count included a higher proportion of votes from urban areas, which favor Fujimori, so Humala's lead would be expected to widen as more of the rural vote comes in.
Three survey firms earlier released exit polls and quick counts that all showed Humala winning.
Analysts said it was still too early to rule out a vote recount with the election too close to call, although Humala's followers were already celebrating before the official count.
"Humala Presidente!" supporters in downtown Lima chanted, waving red and white flags and dancing in a crowd of about 5,000 people.
"Keiko is done," read one banner as an effigy of her burned. She is the daughter of Alberto Fujimori, who was president throughout the 1990s until his government collapsed under a cloud of corruption and human rights scandals. "Fujimori never again," read another banner.
Humala, 48, has moderated his anti-capitalist views since narrowly losing the 2006 election, but investors still view him warily. Peru's currency and stock market in recent weeks plunged on polls that showed him gaining ground, and they were expected to fall again on Monday if he wins the election.
Finance minister Ismael Benavides told Reuters the government had a "contingency plan" to inject liquidity into markets if they suffer a speculative attack on Monday, even as Humala's campaign reiterated vows to prudently manage the economy.
During a bruising campaign, Humala attacked investor favorite Fujimori, 36, over her father's past, including his decision to shut down Congress to consolidate power in 1992.
The younger Fujimori shot back by warning Humala might dismantle the free-market reforms that were begun by her father and helped spur an unprecedented economic surge over the past decade after years of chaos and guerrilla wars.
The elder Fujimori also defeated a Maoist rebel army but fled into exile in 2000 as his government was hit by scandals. He is now serving a 25-year prison sentence for graft and using death squads against suspected leftists.