The third-ranked Polish side, coached by Stefano Lavarini, had struggled at times during the tournament but finished the group stage with a perfect record, topping Group G.
Belgium, ranked 13th in the world, advanced from second place in Group B.
Poland won a thrilling five-set encounter 3-2 (25-27, 25-20, 25-17, 22-25, 15-10).
After losing a tight opening set, the Polish players bounced back to take the next two, only for Belgium to force a decider.
In the final set, Poland pulled ahead and maintained their lead to secure the victory.
Italy, who earlier defeated Germany 3-0 in Bangkok, will be Poland’s next opponent in the quarterfinals.
(ał)
Source: PAP