Onishchenko was born in 1937 in a village of
Khorol Raion,
Poltava Oblast,
Ukrainian S.S.R. He was a strong swimmer early on and taught at the
Dynamo Sports Club. His first world competition was at the
1967 World Modern Pentathlon Championships where he competed with
Stasys Šaparnis and
Edvard Sdobnikov. The Soviet team won a bronze medal at the event. The following year, he took a silver medal at the
1968 Mexico City Olympics with Šaparnis and
Pavel Lednyov. He went on to win gold five times at the world championships, one as an individual. In 1971, he was awarded the
Merited Master of Sports and in 1972, he received the
Order of the Red Banner of Labour. In the
1972 Olympics in Munich, he competed with the Soviet team of Lednyov and
Vladimir Shmelyov that captured the gold. Onishchenko himself took an individual silver medal in the event, finishing behind
András Balczó of Hungary.
1976 Olympics In 1976, the 38-year old Onishchenko entered the Olympics as a three-time world champion but never having won the gold as an individual. Onishchenko was a top fencer and had won gold in the
1974 World Modern Pentathlon Championships in
Moscow. Although he was rated fourth, which would relegate him to being a reserve, Onishchenko won a preliminary tournament in the Soviet Union that pushed him onto the team. After the first event of the pentathlon, the Soviet team found itself in fourth place, trailing closely behind
Britain.
Fencing was the next event: a one-touch
épée tournament. During Onishchenko's bout with British team captain
Jim Fox, the British team protested that Onishchenko's weapon had gone off without actually hitting anything. In fact, Onishchenko's épée was in the air away from Fox when the hit was registered. Fox requested an examination of Onishchenko's weapon, which was found to be faulty, resulting in points being deducted from Onishchenko's score. However, the British team filed an official protest and demanded further examination. Two months later it was reported he had been called before Soviet leader
Leonid Brezhnev for a personal scolding. ==Post-fencing life==