Upon graduation from Villanova, Melchionni was a 2nd-round (19th) overall pick by the
Philadelphia 76ers in the
1966 NBA draft. Melchionni joined the
Phillips 66ers AAU Elite team before returning to his hometown to join the
Philadelphia 76ers in 1966–1967. Immediately, Melchionni was a key reserve on what is, statistically speaking, the greatest 76ers team ever, the 1967 NBA champions led by
Wilt Chamberlain,
Luke Jackson,
Hal Greer,
Chet Walker,
Billy Cunningham, and fellow Villanova alum
Wali Jones. The team was coached by another AAU Elite alum,
Alex Hannum. Melchionni played in 71 games, averaging 4.3 points and 1.3 assists for the championship 76ers. After another season in Philadelphia, Melchionni then played for the Trenton Colonials of the
Eastern Professional Basketball League in 1968–1969. In 1971–1972, Melchionni suffered a broken hand. In his Nets career, he played alongside
Rick Barry and a young
Julius Erving. After the Nets drafted future ABA All-Star
Brian Taylor in 1972, Melchionni became a key reserve player on the 1974 and 1976 ABA championship teams. He averaged 12.4 points and 6.1 assists in seven seasons with the Nets. In his entire career, Melchionni averaged 10.6 points and 5.0 assists in 646 games. Of his career, Melchionni said, "With Julius, we won two ABA titles. To be able to say I played with and won championships with Wilt and Julius, arguably two of the top 10 players in basketball history, means something special to me." ==Post-playing career==