Sandrine Gruda scored 17 points and American Cappie Pondexter added 16 as Ekaterinburg made it seven wins out of seven in the group stages.
It was Lotos who made the early running as Ivana Matovic scored the first six points of the game with a trio of jump shots, but Ekaterinburg battled back to tie it 13-13 by the end of the first quarter and Lotos would never lead again.
An 8-0 run for the hosts, started when Yelena Leuchanka's free-throw tied it at 13, gave Ekaterinburg a 20-13 edge and it looked as though they would go on to dominate the rest of the way.
Lotos did come back one more time, though battling their back through the third quarter to tie the game at 40-40 when Monique Currie sank a pair of free throws.
But Pondexter responded with a three-pointer and Ekaterinburg began to pull away once more, using a 14-3 run that continued into the fourth quarter to give them all the cushion they would need.
Maria Stepanova also made double figures for Ekaterinburg with 10.
Matovic led Lotos with 20 points and nine rebounds, while Magdalena Leciejewska added 10.
The normally reliable Alana Beard was held to just three points, all from the three point line, as she missed all seven of her shots from the field.
The loss leaves Lotos last in Group C with a 2-5 record.
Jacek Winnicki, Lotos PKO BP head coach:
"Our team and UMMC have different goals - they want to reach the Final Four and our goal is just not to finish last in our group. It was not a bad game for us even though the 18 points difference in the final score doesn't reflect this."
Laurent Buffard, UMMC head coach:
"We knew it was going to be a difficult game. The Lotos players are in good shape and that makes them dangerous for us. At the beginning we lacked concentration and that's why we missed a lot of shots. Marchanka, Beard and Currie caused a lot of problems for us. Matovic had a very good game but we managed to deal with it. All in all we showed a better game in the second half."