Panathinaikos edged out Panionios by just one point at Nea Smyrni on Sunday and Olympiakos thrashed Kavala three days earlier in the game postponed from the penultimate round of Basket League games due to the winners' commitments in the Euroleague.
The Panathinaikos victory with an 82-81 score came amid ugly scenes of crowd violence. The match was stopped half a minute before the end for about half an hour as home fans hurled bottles, coins and even pieces of marble.
The stands were evacuated and Panathinaikos won courtesy of a Mike Batiste basket four seconds from time.
Olympiakos is just a win away from clinching the top spot of the regular season after dismantling visiting Kavala 85-60, and needs victory at Ilissiakos on Wednesday to secure home advantage throughout the playoffs.
Meanwhile Panathinaikos captain Dimitris Diamantidis was voted the Most Valuable Player of the Euroleague quarterfinals. CSKA Moscow's former NBA star Andrei Kirilenko came in second.
In the women's game, Athinaikos won its third consecutive Greek Cup on Sunday, beating Esperides Kallitheas 57-50 in the final.