Panathinaikos lost 1-0 at Levadiakos, giving defending champion Olympiakos a chance to narrow its five-point gap with the Athens club.
Substitute Pashalis Melissas headed past goalkeeper Orestis Karnezis in the 83rd minute, a minute after taking the field.
Giannena won 2-1 in Kerkyra and OFI beat Ergotelis 1-0 in Crete.
Olympiakos travels to Thessaloniki on Sunday to face third-placed PAOK.
Watch from Sport.gr:
Levadiakos - Panathinaikos
Kerkira - PAS Giannena
Ergotelis- OFI