BORYSPIL, Ukraine — Vitali Klitschko, the world heavyweight boxing champion, stood on an outdoor stage — gloves off, sport coat on — pounding away, oratorically, in his bid to win a large number of seats for his party in Ukraine’s parliamentary elections on Sunday.

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.