Hubert Hurkacz opened the tie by beating Tallon Griekspoor 6-3, 7-6 in the men's singles, dominating on serve with 21 aces, Polish state news agency PAP reported.
Poland's world No. 2 Iga Świątek then sealed the tie with a 6-3, 6-2 win over Suzan Lamens in the women’s singles.
In the mixed doubles, Katarzyna Kawa and Jan Zieliński completed the sweep with a 6-3, 3-6, 10-4 victory over Demi Schuurs and David Pel.
Poland will play Australia on Friday for a place in the semifinals.
Poland are two-time United Cup finalists, losing the title match to Germany in 2024 and to the United States in 2025.
Team Poland stand for the national anthem at the 2026 United Cup mixed-teams tennis tournament in Sydney, Australia. Photo: EPA/MARK EVANS
The United Cup serves as a warm-up event to the Australian Open, which begins on January 18 in Melbourne.
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Source: IAR, PAP