CSKA ground out a 77-76 home win over plucky Red Star Belgrade while Fenerbahce vindicated several years of heavy investment in a 100-78 whitewash of holders Real Madrid in Turkey.
Serbia playmaker Milos Teodosic sank Red Star with a crucial three-pointer in the final minute, swinging a see-saw contest the Russian side's way.
"They pushed us down to the wire and we now have to get ready to play our best basketball in the next game," said CSKA's power forward Kyle Hines, who topped the scoring with 19 points.
Guard Nando De Colo and small forward Cory Higgins added 13 each for the home side, who will now prepare for a raucous reception in Belgrade's Kombank Arena when the contest moves to Serbia next week.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Real, the royalty of European club basketball seeking a record-extending 10th title, face the daunting task of repelling potent and fired-up challengers.
Fenerbahce, who lost to Real in last year's semi-finals, look a different prospect this season and one capable of becoming the first Turkish side to win Europe's premier club competition.
Despite the absence of influential Czech centre Jan Vesely, Fenerbahce followed up Tuesday's mature 75-69 win in game one with an effervescent performance.
Galvanised by their fervent fans, the home side raced into a 46-17 lead midway through the second quarter as a versatile attack kept finding chinks in Real's ageing armour.
Lokomotiv Krasnodar are at home to Barcelona and Laboral Kutxa Vitoria entertain Panathinaikos, who have six titles, in game two of the other quarter-finals on Friday.
The playoff winners advance to the May 13-15 Final Four in Berlin.
(Editing by Ed Osmond)
