Brno's 83-76 all but eliminated Riga from contention for the next phase.
Though both can still finish with 4-6 records depending on next week's results, Gambrinus would win the tie-breaker because of a superior goal differential in their games against the Latvians.
At one stage, play-off basketball looked as if it might disappear for Brno.
They led for much of the second half but Riga tied the contest at 73-73 with 5:16 left on an Essence Carson jump shot.
Brno responded in grand style.
Hamchetou Maiga Ba made a lay-up, Petra Kulichova split two at the free throw line and Hana Horakova went in for a lay-up to take her points haul to 20 for a 78-73 lead with 3:50 to play.
The Czech giants, finalists in last season's competition, pulled away for a seven-point triumph.
Horakova finished with 23 points while Tamika Whitmore scored 22 and pulled down 10 rebounds.
Eva Viteckova also had 20 points for Brno.
Carson scored 33 for Riga.