BC Khimki stunned defending Euroleague champions Real Madrid with a 85-82 away win over the Spanish side on Wednesday.
Madrid had won their last 14 games at home but lost to the Russian team for the second time in the 2015-16 competition thanks in part to 18 points from point guard Tyrese Rice.
Khimki led by as much as 10 points in the second quarter but went into half-time with just a two-point advantage.
A technical foul on Madrid coach Pablo Laso allowed Rice to make it 79-74 in the fourth quarter, but three-pointers from Sergio Rodriguez (17 points) cut the gap to two points with a minute left.
But Madrid could not complete the fightback as the teams traded free throws, with Khimki holding on for a fourth Group A win.
Madrid have won just two games face an uphill battle to qualify for the Top 16.
However, Laso said: "I am not especially worried about the standings; we know we will qualify if we win all four games, that we may not qualify if we win three, but also that we may qualify with two wins, too.
"I am worried about our next game, but the feeling I get is good and we should not be afraid of anyone."