A youthful state governor is set to give Hugo Chávez a tough battle for Venezuela's presidency after sweeping the opposition nomination in primary elections.

Henrique Capriles, 39, crushed four rivals in a nationwide landslide after styling himself as the candidate with the best chance of unseating Chávez in October's presidential election.

The governor of Miranda state, which includes most of the capital, Caracas, won more than 62% of the vote and was immediately endorsed by the defeated candidates, who vowed to make him the next president. Jubilant supporters honked car horns, chanted "unity" and waved yellow flags, the colour of Capriles's party, Primera Justicia.

"This is not the hour of the left or the right but the hour of Venezuela, of all Venezuelans," he told a victory rally, repeating a non-confrontational, ideology-free theme aimed at the centre, a strategy partly modelled on Brazil's ruling party.

"This project," he said, referring to Chávez's so-called socialist revolution, "belongs in the past." He called Venezuela a country in crisis, citing economic and social problems and political polarisation.

With the vote 95% complete on Sunday night, Capriles had won 1.8m of 2.9m votes, more than double his nearest challenger. Just as important as his margin, said analysts, was the unexpectedly high turnout for a primary, showing the opposition base was mobilised and itching to take on Chávez. There are around 18 million registered voters in Venezuela.

"A tsunami called Capriles" ran a banner headline on the website noticias24.com. "Hugo Chávez is not a happy camper tonight," said the blog Caracas Chronicles.

The scale of the victory will give Capriles momentum as he begins an eight-month marathon campaign against the president's formidable charisma and electoral machine. After 13 years in power the 57-year-old incumbent remains popular, with ratings over 50% making him favourite to win in October. But the same polls suggest concerns over violent crime, inflation and crumbling infrastructure could cost Chávez a third six-year term.

Chávez, who says he is cured from a cancer diagnosed last year, is already in full campaign mode, announcing new oil-funded social programmes and shoring up old ones in the urban slums where most Venezuelans live. After a break during cancer treatment he has resumed giving epic speeches, many of which all radio and television stations are obliged to transmit live. An address to the national assembly last month set a new record: nine and a half hours.

The former tank commander has dismissed the opposition as "oligarchs" and "US imperialist lackeys" who take orders from Washington and plan to destroy the advances of what he terms a 21st-century socialist revolution. He suggested he would not debate his rival for the presidency: "An eagle does not hunt flies."

Anticipating a Capriles victory, state media have portrayed him as a spoilt scion of the discredited rightwing elites that preceded Chávez. The governor, a bachelor with a lean runner's physique, comes from a rich family and dated a famous model.

He won successive posts – as a legislator and a mayor, before toppling a senior Chávez lieutenant in Miranda – by projecting a pragmatic, can-do image. He scoots around Caracas on a motorbike to dodge perpetual gridlock.

Polls suggest Venezuela is divided into a third who adore Chávez, a third who loathe him and a floating third. Chávez has in the past benefited from intense polarisation that has seen the opposition alienate voters by staging a coup, general strikes and an election boycott.

Since 2006, when Chávez swept to a second term, the opposition has slowly clawed back support, winning governorships and mayorships in poor urban areas such as Petare, once a "chavista" bastion, on the promise of improving security, rubbish disposal and pothole-filling.