Mareks Jurevicus erupted for 29 points for Ventspils, including 13 made free throws from 15 attempts, and also corralled nine rebounds.
The Latvians improved to 2-3 with the victory and still have a chance of overtaking Cajasol Sevilla (2-2), who were in action later on against Group A leaders Belgacom Liege Basket (4-0).
Ventspils opened up a nine-point advantage late in the third quarter but Energa Czarni clawed their way back early in the fourth.
Demetric Bennett hit back-to-back baskets and his Energa teammate Marcin Sroka stroked a three-pointer to make it 65-63.
Janis Strelnieks replied with a three-pointer for the home side, though, starting a 13-3 run as Ventspils took control for good.
Pawel Leonczyk had 19 points and Mateo Kedzo 18 for Energa, who dropped to 1-4 and saw their hopes of reaching the Top 16 die.