On Tuesday, Karsiyaka slumped to a shock 76-74 defeat at home to Paris Levallois, despite a double-double display by Thomas, who finished with 25 points on 10-for-15 shooting from the floor, 10 rebounds and two assists in 35 minutes of playing time.
The American power forward registered an efficiency index rating of 29 and earned quarter-final play-offs Game 1 MVP honours.
Even more memorably, the moment Thomas grabbed the third of his 10 boards on the night, he also became the first player in the history of the EuroChallenge to collect 500 rebounds.
The 26-year-old is playing in his fifth consecutive season in the European competition and has been among the top rebounders every year.
He averaged 8.2 rebounds per game in each one of his two seasons with Belgacom Liege, 6.6 rebounds in the 2011 campaign with another Belgian club, Telenet Oostende, and 11.3 rebounds last season with Georgian club Armia.
Tuesday's double-double was the third in this EuroChallenge season for Thomas, who is the eighth-leading rebounder with 7.5 rebounds per contest and also contributes 13.8 points and 1.8 assists on average.
Dwight Buycks of BCM Gravelines scored 18 points and dished out eight assists in his team's 86-57 rout of Joensuun Kataja on Tuesday and registered an efficiency rating of 27 to come in second after Thomas in Game 1 of the quarter-finals.
Meanwhile a débutant in this season's EuroChallenge earned third place, as veteran Lamayn Wilson, who only joined Krasnye Krylia last week, contributed 12 points, nine rebounds and two blocks in his team's 80-60 win over Telekom Baskets Bonn.
EUROCHALLENGE QUARTER-FINAL PLAY-OFFS GAME 1 EFFICIENCY INDEX - TOP 10