Panathinaikos beat PAOK 1-0 to clinch the Greek Cup on Saturday in match marred by crowd trouble as rival fans threw flares and clashed with police inside the Olympic stadium.
Violence broke out an hour before the match was due to start as spectators began arriving at the stadium, delaying the kickoff.
Panathinaikos and PAOK fans tried to enter the area of empty seats separating them, and riot police responded with tear gas to break up the crowd.
The final was interrupted after Aitor Cantalapiedra scored from the penalty spot for Panathinaikos in the 34th minute and PAOK fans threw objects onto the pitch.
PAOK fans also clashed with police outside the stadium during halftime, a police official said.
Greek soccer has been plagued by violence on and off the pitch and authorities have repeatedly promised to clean up the game. Fights between football fans are frequent before or after a game and it is not uncommon for a match to be disrupted by crowd trouble or a pitch invasion, despite the heavy fines.
The government has tightened rules to combat violence at sports events following the killing of a 19-year-old soccer fan this year in what was believed to be an attack by rival supporters.