Kostas Sloukas had 14 points for Olympiacos at the Peace and Friendship Stadium in Piraeus.
Giannoulis Larentzakis, Moustapha Fall and Tyler Dorsey each added points.
Jan Vesely was the high scorer for Fenerbahce Beko with 14. Marko Guduric and Nando de Colo had 10 points apiece.
Fenerbahce Beko suffered their fifth defeat in seven games.
Olympiacos sealed their fifth victory of the season.
Thursday results:
Alba Berlin - Bayern Munich: 69-82
Olympiacos - Fenerbahce Beko: 67-65
Maccabi Playtika Tel Aviv - Barcelona: 85-68
AX Armani Exchange Milan - Crvena Zvezda: 79-62
