Last season's finalists CSKA Moscow eased to an 89-78 home win over Caja Laboral Vitoria, eight-time winners Real Madrid thumped Maccabi Tel Aviv 79-53 and 2010 champions Barcelona scraped a 72-70 victory over Panathinaikos Athens.
Printezis, who sank the game-winning shot on the buzzer for Olympiakos in the 2012 final in Istanbul, was again instrumental for the Greek side with 26 points in a physical encounter against Efes.
He was the only player in double digits for the winners, whose iron-clad defence forced the visitors to hit only one of 19 three-point attempts and saw former NBA guards Jordan Farmar and Sasha Vujacic combine for a slim total of 12 points.
CSKA were in control from start to finish against Caja and a balanced team effort saw them carve out a whopping 24-point lead in the final quarter before the Basque outfit salvaged some pride with a late rally.
Former Toronto Raptors sharpshooter Sonny Weems led CSKA with 19 points, Serbia playmaker Milos Teodosic added 17 while his compatriot Nenad Krtsic and Russia centre Sasha Kaun chipped in with 16 each.
The home team's Italian coach Ettore Messina, who steered CSKA to two titles in Europe's flagship club competition during his first spell in charge 2005-2009, was unhappy with his team's defence.
"The team efficiency ranking says we had a lot of great moments but we also allowed Caja to score 69 percent of their two-point shots, which is unacceptable and tell us that we still have to improve," Messina told the competition's official website (www.euroleague.net).
Kaun added: "It's a short series so we can't allow ourselves to make so many mistakes, we lost concentration in some parts of the game and we will try not to do that any more."
Maccabi made a bright start against Real and led 26-14 midway through the first half before the hosts turned the match on its head with a stunning 24-1 run which threw the home fans into raptures.
Versatile shooting guard Rudy Fernandez led Real with 15 points and Montenegrin-born forward Nikola Mirotic nailed 14 as the home team's entire 11-man roster got on the scoresheet.
Barcelona missed four key players through illness or injury and eked out their victory after Panathinaikos centre Stephane Lasme missed a pair of free throws in the dying seconds of overtime, spoiling a fine individual performance garnished by 14 points and four rebounds.
"This game is over and we have to focus on the next one," said Lasme. "Barcelona are a great team and a performance like this is a confidence booster, hence we should take as a positive the fact that we were in the game the whole time."
The playoff winners will advance to the May 10-12 Final Four in London's O2 Arena.
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