Olympiakos grabbed a precious 84-82 home win over Caja Laboral on December 8 to boost its chances of qualifying to the top 16 of the Euroleague.
The match at the Peace and Friendship Stadium in Piraeus was evenly balanced with the Greeks and the Spaniards sharing the lead.
A great second period saw the hosts recover from a 10-point deficit to end the first half with a 46-41 lead.
Mirza Teletovic, who scored of 32 points, almost single-handedly put the Basques on level terms again, but the Reds were not to be denied on the night.
They may end up regretting having let a seven-point advantage shrink to just two points in the end, exactly the same margin as their loss in the first match between the two sides at Vitoria. That means they are now trailing the Basques on overall points difference, as they both have four wins and four losses.
Vassilis Spanoulis topped the scoring chart for Olympiakos with 21 points. Costas Papanikolaou added another 12 while Kyle Hines and Giorgos Printezis scored 11 apiece.