Making a limited number of international tournament appearances, he was successful at
Ulan Bator (1965) and
Zinnowitz (1966). The latter was probably his finest moment, scoring +8−1=6, to take first place among reasonably strong opposition, including
Victor Ciocaltea and
Wolfgang Uhlmann. Aside from Zinnowitz,
Hartston notes that Antoshin's results were never outstanding. His other results were nevertheless respectable; 2nd at Kienbaum (Berlin) 1959 (Uhlmann won), 5th at Moscow 1960 (ahead of
Polugaevsky,
Hort and Uhlmann), 4th at
Sochi 1963, 4th at Moscow 1963 (ahead of
Keres,
Liberzon,
Szabó and Hort), 6th= at Sochi 1964, 2nd at
Venice 1966 (
Ivkov won) and 4th at
Havana 1968 (The
Capablanca Memorial). He regularly played at Sochi, but finished lower on other occasions. His tournament appearances were less frequent in the 1970s. He did, however, share 3rd place at
Sarajevo in 1970 and placed runner-up at
Frunze in 1979. A major reason for his limited progress as a player was his continued amateur status. He became a tournament organiser and trainer to the USSR Olympiad team, maintained a second career as a technical designer, and according to Cafferty & Taimanov, was also supposed to have strong links with the
KGB. On numerous instances, he travelled abroad with the Russian chess players as a
coach but refused to attend to the coaching duties citing that he was there for missions
other than the chess coaching. At the
Soviet Championship, he had moderate results, participating in 1955, 1956, 1957, 1967 and 1970. His highest placing was a share of sixth in 1967. ==Theory==