Career
In 1919, he took 2nd, behind František Schubert, in Prague (Czechoslovak Chess Championship). In 1936, he took second place, behind Henryk Friedman, in Vienna. In 1937, he took second, behind Karl Gilg, in Teplice (Teplitz Schönau).
In 1938, he tied for first with Hermann in Prague (CSR-ch).
Karel Opočenský played for Czechoslovakia four times in the Chess Olympiads. In 1931, he played at fourth board in 4th Chess Olympiad in Prague (+7 –2 =4).
In 1933, he played at fourth board in 5th Chess Olympiad in Folkestone (+10 –0 =3). In 1935, he played at second board in 6th Chess Olympiad in Warsaw (+5 –4 =6).
In 1939, he played at first board in 8th Chess Olympiad in Buenos Aires (+8 –5 =4).
When World World War II broke out, Opočensky, January Foltys, and František Zíta were playing for the Bohemia & Moravia team in the 8th Chess Olympiad in Argentina. They chose to return home, whilst team-mates Jiří Pelikán and Karel Skalička elected to remain in South America. In 1940, Opočensky took second, behind Foltys, in Rakovnik (Bohemia and Moravia-ch).
In 1942, he tied for fourth-fifth in Prague (Duras Jubileé) behind joint winners, Alekhine and Klaus Junge.
After the war, he played in several international and local (Czechoslovakia) tournaments. In 1945, he tied for second-third, behind Emil Richter, in Prague.
In 1946, he took fourth in London. In 1946, he tied for first with Daniel Yanofsky and Pachman, in Arbon.
In 1947, he took fourth in Vienna.
In 1949, he tied for third-sixth in Vienna. In 1949, he tied for fourth-fifth in Arbon. In 1951 and 1954, he was the chief arbiter for the World Chess Championship matches in Moscow, and also in the 10th Olympiad at Helsinki 1952, and in the second Candidates Tournament at Zurich 1953.
Opočenský is also known as a theoretician.
There are two opening variations named after him: the Opocensky Variation in the Grünfeld Defence (1d4 Nf6 2c4 g6 3Nc3 d5 4e3 Bg7 5Nf3 O-O 6Bd2) and the Opocensky Variation in the Sicilian Defence (1e4 c5 2Nf3 d6 3d4 cxd4 4Nxd4 Nf6 5Nc3 a6 6Be2). Awarded the IM title in 1950, he became an International Chess Arbiter in 1951.