Real, chasing a record-extending 10th title, are level with four other teams on six wins and six defeats in their Top 16 section.
Leaders CSKA Moscow have booked their playoff berth with two games to spare and Laboral Kutxa Vitoria are favourites to join them, with both sides possessing an 8-4 record.
Real, Barcelona, Khimki Moscow, Olympiakos and Germans Brose Baskets Bamberg are all in the chasing pack.
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In the other group, Anadolu Efes Istanbul kept alive their hopes of advancing with an 87-67 home win over Unicaja Malaga while eliminated Cedevita Zagreb crushed already-qualified frontrunners Fenerbahce Istanbul 89-59.
Roared on by a fervent home crowd in their Peace and Friendship Arena, Olympiakos carved out a 53-33 first-half advantage against a subdued Real.
The Greek side, who won successive titles in 2012 and 2013, nailed 11 three-pointers from 23 attempts as shooting guard Vangelis Mantzaris led the charge with 19 points.
Khimki stayed in the hunt with a 76-71 victory at 1999 champions Zalgiris Kaunas thanks to 17 points from playmaker Tyrese Rice and 15 by Finnish guard Petteri Koponen.
Anadolu Efes had to beat Unicaja to avoid elimination and were helped by a strong first quarter in which they engineered a 27-11 advantage.
Croatian forward Dario Saric and French guard Thomas Heurtel netted 17 points each for the Turkish team who sank 12 of their 23 shots from three-point range.
Having already secured their passage and home court advantage in the playoffs, Fenerbahce produced a listless performance in Zagreb where Marko Arapovic inspired the home side with 18 points.
The Top 16 features two pools of eight teams with the leading four from each section advancing to the best-of-five quarter-final playoff series.
The winners progress to the May 13-15 Final Four in Berlin.
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