Ukrainians are widely expected to give a resounding endorsement to the overthrow of their last elected leader by voting on Sunday for presidential candidates promising close ties with the West, in defiance of Russia's Vladimir Putin.
But the absence of more than 15 percent of the electorate, in Russian-annexed Crimea and two eastern regions where fighting with pro-Moscow rebels continued on Saturday, may mar any result - and leave the Kremlin questioning the victor's legitimacy, for all of a pledge by Putin to respect the people's will.
European election monitors largely pulled out of Donetsk region for their own safety, citing a campaign of "terror" by pro-Russian separatists against Ukrainian electoral officials.
Polls make a billionaire confectionery magnate known as the "chocolate king" an overwhelming favourite in a vote expected to show a high turnout on a warm, sunny day. For many the biggest question is whether Petro Poroshenko, who has been a minister in the past, can take more than 50 percent to win outright in one round.
Poroshenko, 48, was a strong backer of the protests against Moscow-backed president Viktor Yanukovich last winter and has sought a quick victory by warning that new unrest might prevent a second voting round.
His closest, if distant, rival is former prime minister and wealthy former businesswoman Yulia Tymoshenko, who is 53 years old. She seems best placed to contest a runoff in three weeks but remains a divisive figure to many: more closely associated than Poroshenko with the economic failures and rampant corruption that have marred Ukraine's 23 years of independence from Soviet rule.
Officials say many polling stations in Ukraine's Russian speaking regions will not open for fear of attack and only early on Sunday will they try to distribute ballot papers to those areas where voting may be possible.
Voting will start at 8 a.m. (0500 GMT) and end 12 hours later. Exit polls at 8 p.m. (1700 GMT) will indicate the result and an official outcome is due before international monitors deliver their verdict on the process on Monday afternoon.
Western states backed those who took power when Yanukovich fled to Russia three months ago after street protests triggered by his rejection of a free trade agreement with the EU. They hope that an electoral mandate for a new leader can help resolve a confrontation with Russia that has sparked military buildups east and west of Ukraine and raised fears of a new Cold War.
Putin pledged on Saturday to "respect" the people's choice and work with Ukraine's new administration - a conciliatory promise made during an economic forum at which he acknowledged U.S. and EU sanctions over Ukraine are hurting the Russian economy.
But he defended his annexation of Crimea in March as a response to the democratic will of the majority ethnic Russian population there. Kiev and its Western allies accuse Moscow of a propaganda war to sow fear among Russian speakers in eastern and southern Ukraine of "fascist" Ukrainian nationalists and of supporting rebel forces that have seized many towns in the east.
Two weeks ago, separatists in the Donetsk and Luhansk regions held referendums they said let them break from Kiev and opened a way to possibly following Crimea into union with Russia. Moscow denies any plan to seize more Ukrainian territory, despite a substantial build-up of its troops on its frontier with Ukraine.
Opinion polls before the last few months of violence showed disillusion with Kiev's politicians in the Russian-speaking, industrial east but limited appetite for outright secession.
Putin played down talk of a return to Cold War with the West and dismissed the idea he was bent on restoring the former USSR, whose collapse he has in the past lamented. Europeans fear a resurgent Moscow dismissive of civil rights, but Putin said he was only asserting Moscow's right to be treated as an equal.
Washington and its EU allies are concerned that while Russia may accept the election result, it may use influence in eastern Ukraine to undermine the new president's authority and keep the country beholden to Moscow. Russian officials have questioned the value of holding the vote when the east is in "civil war."
Ukraine, with 45 million people, is the second most populous ex-Soviet state and plays a pivotal role in the political and economic relations between Russia and the EU.
Large volumes of Russian natural gas flow across it to Germany and other consumers, creating mutual dependencies that complicate diplomatic calculations on all sides of the conflict.
The inheritor of a historical patchwork of regions variously ruled from not only Moscow but by Poland, Austria and others, Ukraine has a mix of Russian and Ukrainian speakers as well as many ethnic minorities, all of whom have struggled to forge a common national purpose. Polls have consistently shown a majority supporting independence and good ties with both east and west.
Since the "Orange Revolution" in 2004, Ukrainians of all stripes have been disappointed with the subsequent decade of economic drift and corruption, arguably the worst in Europe. Their hopes are now pinned on Sunday's vote to turn that around and start history afresh.
Few of the leading candidate are new faces, however.
Poroshenko and Tymoshenko played leading roles in the administrations that preceded Yanukovich's defeat of Tymoshenko in the 2010 election. Poroshenko later even held a cabinet post for a time under Yanukovich.
Both became wealthy in the anarchic post-Soviet 1990s. Poroshenko is now worth $1.3 billion, according to Forbes, through his candy and chocolate empire, while Tymoshenko made money as the "gas princess" through her involvement in the trade and transit of Russian natural gas.
After the Orange Revolution, when he was head of the national security council and she prime minister, the two traded mutual accusations of corruption. Tymoshenko was jailed for corrupt gas deals with Russia under Yanukovich but was released when he was toppled and her record was cleared of any blame.
Olga, an 82-year-old pensioner out for a walk in central Kiev on Saturday, said she thought Poroshenko could make the best attempt at ending six months of agitation and uncertainty.
"He is a businessman," she noted doubtfully as she strolled with her husband, Nikolai, across Independence Square, known as Maidan, where militant anti-Yanukovich protesters are still camped out, determined to hold new leaders to their promises.
"But he'll be good for the state and the people. He has factories near us and created jobs. He can calm things down."
But in the easternmost city of Luhansk, would-be voter Oleksander Cherednichenko doubted whether people there would be able to take part at all: "People are afraid that if they do go to a polling station that there will be gunmen there," he said.
"The best case scenario is that gunmen will just tell them to get out. The worst case scenario is that they shoot them."
(Additional reporting by Gabriela Bazcynska in Mariupol and Gareth Jones and Yvonne Bell in Kiev; Writing by Alastair Macdonald; Editing by Steve Orlofsky)