Ventspils broke away right from the get-go, starting the game with an 8-0 stretch and going on to establish a 26-15 lead after the first quarter.
The nightmarish start for Siauliai continued in the second period, as Lorenzo Williams and Janis Timma guided the defending BBL champions into a 50-25 halftime advantage.
The second half was merely formality, but Ventspils kept pulling away and led by as many as 46 points in an unexpected blowout.
Lorenzo Williams had a team-high 19 points, seven rebounds and five assists, Janis Timma scored 18 points and dished out six dimes, while Maris Gulbis added 17 points.
For Siauliai, Vytas Sulskis collected 21 points and eight rebounds, Darius Pakamanis scored 12 points, with no other players in double figures.