Olympiakos beat Villeurbanne on Friday and rose to the top of the Euroleague standings, while Panathinaikos lost precious ground losing to Hapoel Tel Aviv away.
With three more games to play till the end of the regular season, the Reds have returned to the summit courtesy of their 82-74 victory in France against host ASVEL.
The French, who are bottom of the table, posed a greater-than-expected challenge to the Greeks, but could never really get any closer than three points in the second half (61-58).
After staying sidelined due to injury for 10 long months, Moustapha Fall returned to the Olympiakos squad on Friday, but did not get to play in this game.
Sasha Vezenkov made 23 points and Donta Hasll 14 in this 23rd win of Olympiakos in 35 games.
On the contrary, Panathinaikos wasted a great chance for victory in Sofia on Thursday, losing 92-88 to Hapoel, in a court that had thousands of Panathinaikos fans at the stands and felt like a home game for the Athens giant.
Pushed on by its supporters, Panathinaikos had a good first half and an excellent third quarter that saw it lead by up to 12 points (75-63).
Yet somehow the last period was disastrous for the Greens, who conceded 29 and scored only 13, with Kendrick Nunn being unable to make any of the crucial shots in the last few possessions.
Panathinaikos is now seventh, with a 20-15 record, after having Juancho Hernangomez score 17 points and Nunn 15.