Nicknamed Pillín and El Primer Crack, Furlong started playing basketball and tennis at the Gymnastics and Tennis Club of Villa del Parque. He later concentrated in basketball, in the youth divisions of Club Gimnasia y Esgrima de Villa del Parque. After his debut with the first team in 1944, Furlong won 6 Torneo Metropolitano Buenos Aires League titles (1945, 1946, 1947, 1948, 1951, and 1954), in the amateur league that was run by the Argentine Basketball Federation. In 1953, Furlong began attending Southern Methodist University, where he played college basketball with the SMU Mustangs. He graduated in 1956, after reaching the 1956 NCAA Final Four, while playing alongside All American, and future NBA player, Jim Krebs.
In 1957, while playing club basketball for Villa del Parque, Furlong was forced to take an early retirement from the sport, at the age of 30, after the new Argentine military government and Amador Barros Hurtado (President of the Argentine Basketball Federation), made the controversial decision that all members of Argentina's FIBA World Cup team should be considered professional, as they had breached the 'Amateurism Code' of the IOC, after receiving cars as gifts. On 8 January 1957, all the members of the Argentine FIBA World Cup team were banned for life, from participation in basketball. Juan Perón had previously left the country, to escape the coup d'état of his presidency.
Furlong later played tennis, where he eventually attained a seventh place in the Argentine national rankings. In 1966, he joined the committee of the Argentine Tennis Association (AAT), becoming vice-president, and eventually coach of the Argentine Davis Cup team. In 1977, his last year as a tennis coach, his team reached the semifinals of the 1977 Davis Cup.