Campomanes was a National Master strength player during his peak years, and was Philippine national champion on two occasions (1956, 1960). He represented his country at five Chess Olympiads: Moscow 1956, Munich 1958, Leipzig 1960, Varna 1962, and Havana 1966. He met some distinguished opposition as a result, losing games against Pal Benko and Ludek Pachman at Moscow 1956, Oscar Panno at Munich 1958, Mikhail Tal and Miguel Najdorf at Leipzig 1960, and Lev Polugaevsky at Havana 1966.