[1] Kefalos attended John Bartram High School, in Philadelphia, Pennsylvania, in the US.
Kefalos won Philadelphia's high school city basketball championship in 1961.
[8] After graduating from college, Kefalos was offered a contract by the Seattle SuperSonics of the National Basketball Association (NBA).
[9] He eventually began his club career with the Wilmington Blue Bombers of the Eastern Professional Basketball League (EPBL),[10] which would later be known as the Continental Basketball Association (CBA), in the 1968–69 season,[11] in which he averaged 6.4 points, 3.8 rebounds, and 4.0 assists per game, in 25 games played.
Panathinaikos' head coach at that time, Kostas Mourouzis decided that he wanted to sign Kefalos, and also advised the-then head coach of the senior Greek national team, Faidon Matthaiou, to invite Kefalos to participate in the training of the Greek national team.
Kefalos ended up moving from the US to Greece, and joining Panathinaikos' basketball team for the 1969–70 season.
He was also a member of the Panathinaikos team that made it to the semi-finals round of Europe's top-tier level European-wide club competition, the FIBA European Champions' Cup, which is now known as the EuroLeague, in the 1971–72 season.