Anwar Ibrahim said only fraud can stop his Malaysian opposition from scoring a historic election win as the rival sides launched a last-ditch campaign blitz Saturday on the eve of a tense vote.
Sunday's elections are the first in the country's 56 years of independence in which the only government Malaysia has known faces possible defeat.
The uncertainty has given rise to a bitter campaign, with Prime Minister Najib Razak warning of chaos and ethnic strife under the opposition, which has countered with numerous allegations of government vote fraud.
Anwar set the stage for a possibly destabilising challenge to the results, accusing the Barisan Nasional (National Front) regime of cheating to thwart what he called a "democratic revolution".
"We have advised our supporters to remain calm, not to be provoked, not to take the law into their own hands, support the process," Anwar told AFP in an interview in his home seat in the state of Penang.
He added: "unless there's a major massive fraud tomorrow, that is our nightmare... we will win."
Both Anwar and Najib barnstormed through their home regions where they will cast their own ballots early Sunday.
Najib's ethnic Malay-dominated Barisan has tightly held power in the multi-racial nation for decades, steering it from a backwater to an economic success with some of Asia's highest living standards.
But its grip is slipping amid rising anger over corruption, controversial policies favouring Malays, and authoritarian tactics.
A survey released Friday indicated a race too close to predict, with Barisan and Anwar's three-party Pakatan Rakyat (People's Pact) equal in voter support but with many undecided.
Barisan has launched an all-out blitz, with Najib showering voters with cash handouts from government coffers, as Barisan-controlled traditional media relentlessly attack Pakatan.
In a televised interview late Friday, Najib appealed to voters for a "strong mandate" so he can implement his promise to reform.
"Definitely, with a strong mandate, we can do much better in the next five years," he said.
Anwar was Barisan's heir-apparent until a 1998 power struggle saw him jailed for six years on sex and graft charges widely criticised as trumped-up.
He later brought his star power to the previously weak opposition, dramatically reversing its fortunes.
Upping the ante, Anwar released a 100-day roadmap for Pakatan governance on Saturday, pledging to look into major corruption allegations, free up the media and lower petrol prices.
His transparency promises are anathema to Barisan, which has long been accused of sweeping widespread corruption under the rug.
Under pressure, Najib recently announced limited political liberalisation moves but critics say he has not undertaken deep reforms.
The charismatic Anwar has drawn massive crowds on the stump, including Friday night, when tens of thousands of supporters swamped opposition-held Penang's capital.
Activists warn the election could be "stolen" by Barisan, which has been accused of fraud in past polls.
Last week it was learned that indelible ink meant to mark voters' fingers to prevent multiple voting could be washed off, and Anwar said Barisan was flying tens of thousands of "dubious" voters to pivotal areas.
The government later admitted the flights but called them a "get out the vote" drive.
Violence also has raised tensions, though no deaths have been reported.
In the latest incident, an explosive device detonated at a power substation near the Kuala Lumpur headquarters of Anwar's party late Friday, causing minor damage, a party official said.