Mr. Klitschko, the leader of an opposition party, the Ukrainian Democratic Alliance for Reform, has injected an element of unpredictability into an election that from the outset has seemed heavily tilted in favor of the Party of Regions of President Viktor F. Yanukovich.
Critics here and in the West say the race is distorted by the continued imprisonment of prominent opposition leaders, government manipulation of media outlets and other malfeasance.
But where others see a fixed fight, Mr. Klitschko sees opportunity. With one giant hand wrapped around a microphone, the other occasionally chopping the air, he landed blow after blow against the status quo, lamenting that Ukraine has lagged behind its Eastern European neighbors.
He denounced corruption among the authorities, and insisted that pensions and salaries should be bigger and living standards better. “Six million Ukrainians do not see a future for themselves in this country and are looking for jobs abroad, 70 percent of young people want to leave the country and live abroad,” he told a crowd of about 250 gathered at an athletic field here.
“What future we can talk about?” Wages, he said, should be such “ that for a month’s salary a television set and a washing machine could be bought, a car in five years and an apartment in 10 years.” To applause and chants of “Klitschko! Klitschko!” he declared, “We can do this.”
In a country where politics in recent years has focused almost entirely on the bitter rivalry between President Yanukovich and the jailed former prime minister, Yulia V. Tymoshenko, Mr. Klitschko, 41, is emerging as a serious force.
The acronym for Mr. Klitschko’s party, Udar, spells the word “punch” in Ukrainian, and polls show it surging into second place, ahead of the opposition coalition that includes Ms. Tymoshenko’s party, Fatherland, but still trailing the governing Party of Regions and its allies.
The precise makeup of Parliament, called the Verkhovna Rada, will not be known until weeks after Sunday’s voting because half of the 450 seats will be filled by individual candidates not required to declare a party affiliation. The other half are filled proportionally through voting for party lists.
The election is being watched closely as a gauge of democracy in Ukraine, a former Soviet republic of 45 million, once viewed as on a steady track toward integration with Europe after the Orange Revolution of 2004.
But the country has become increasingly isolated since Mr. Yanukovich’s election in a runoff with Ms. Tymoshenko in 2010.
Control of Parliament will also be a major factor in the higher-stakes presidential contest in 2015.
Mr. Yanukovich’s government has taken aggressive steps to show the elections as fair, even installing Web cameras in more than 30,000 polling stations.
Officials say that Ukraine is being unfairly maligned in the West, largely based on the case of Ms. Tymoshenko, who they insist was legitimately convicted on charges related to the alleged rigging of natural gas contracts with Russia.
Sergey Tigipko, a vice prime minister, said in an interview that Mr. Yanukovich’s administration had steered Ukraine out of the financial crisis, with solid growth since 2010, improvements in social services, and increases in pensions.
Mr. Tigipko said that record would help the Party of Regions win support not just from its base, in the Russian-speaking predominantly east and south of the country, but also in the center and the Ukrainian-speaking west.
“The economic growth and the improvement in social standards should convince people,” Mr. Tigipko said.
But financial analysts say that the country’s economy is in trouble again as a result of flagging demand in Europe, particularly for steel, Ukraine’s main export.
Critics, including senior Western leaders, say Mr. Yanukovich’s government has a long way to go to prove its commitment to democracy.
In an opinion column inThe New York Times this week, Secretary of State Hillary Rodham Clinton and Catherine Ashton, the European Union’s high representative for foreign affairs, described “worrying trends” in Ukraine, including “reports of the use of administrative resources to favor the ruling party candidates.”
But no critic has been as harsh as Ms. Tymoshenko, who looms large in Ukraine’s political life, even from prison.
In an open letter to Mr. Yanukovich this week, she complained about her treatment in prison, saying she was secretly recorded even in the bathroom. “Maybe you get more self-confidence in your political capability by watching a female political opponent naked,” she wrote.
Supporters of Ms. Tymoshenko say they are counting on the European Court of Human Rights to order her release, and on her running again for president.
One of her lawyers, Sergey Vlasenko, said the elections could never be considered fair because Ms. Tymoshenko was barred from the ballot.
“These elections are already fraud,” Mr. Vlasenko said in an interview. “If Ms. Tymoshenko would be free, the campaign would be totally, totally different.”
But analysts say many voters are disenchanted with the familiar choices.
“There is a demand for a new political figure, after disillusionment with the old ones,” said Mikhail Pogrebinsky, the director of the Kiev Center of Political and Conflict Studies, a research group.
Mr. Pogrebinsky said that Mr. Klitschko is famous, though not a traditional politician, and plain-spoken, both advantages. He is also mostly untested, having served in the Kiev City Council and run unsuccessfully for mayor.
His newness — and independent wealth — seemed to appeal to voters in Boryspil, a city of 53,000 about 22 miles from the capital, Kiev, and the location of the country’s main international airport.
On Thursday, supporters stood atop a decommissioned Soviet armored personnel carrier that was repainted bright red with the name of Mr. Klitschko’s party emblazoned in white on its side, and waved flags directing people to his rally.
The after-work crowd was largely receptive, applauding enthusiastically at several points, especially when he criticized what he called the greed of current officials.
Ukrainian news accounts have recently focused on a huge residential compound, with a golf course and other trappings where Mr. Yanukovich lives outside of Kiev
Ilona Musayeva, 40, who sells cosmetics from a stall in a local market, said that she would vote for Mr. Klitschko and that the public did not have to worry about him stealing from taxpayers. “I respect him,” she said. “I think he has enough money.”
Mrs. Musayeva and other Boryspil residents said it was hard for young people to find work, hard for old people to live on their pensions, hard to do much more than struggle to get by.
On stage, Mr. Klitschko said he had ruled out any partnership with the Party of Regions but after the elections might consider an alliance with Ms. Tymoshenko’s party, now led by Arseniy Yatseniuk, 38, a former foreign minister.
Mr. Klitschko insisted that Ukraine should — and could — keep up with its neighbors.
“We promise good salaries, good pensions, good medical care, good living conditions,” he said, to applause and cheers. “Poles could do it. Georgians could do it. And we also can do it. That is why we have engaged in this battle for Ukraine, and I am sure that we shall win it.”