Besiktas had to win by 10 points to eliminate Nanterre, but the French club earned the victory on the road (60-62) and qualified to the BCL quarter-finals.
Besiktas was in front by eight early in the second quarter (32-24), but Nanterre stood tall (34-30) and sealed the deal.
Jeremy Senglin led the winners, with a game-high 18 points. On the other hand, Phil Pressey had a team-high 17 points for the losing squad, with Kyle Gibson posting 15 points and Ivan Buva 13.
Nanterre had defeated Besiktas 68-59 in Game 1.