The United States, Great Britain, Greece, France and Switzerland each swept the first day of play on Thursday in the inaugural United Cup, an 18-team, mixed-gender competition being played in a trio of Australian cities.

The hard-court tournament is being sponsored by the ATP and WTA tours and features teams competing for $15 million in prize money. The group stage runs through Jan. 3 with playoffs to follow. The final will be held Jan. 8 in Sydney.

In Group A competition, held in Perth, Team Greece swept Bulgaria. Stefanos Tsitsipas bested Grigor Dimitrov in three sets, 4-6, 6-2, 7-6 (4). Despina Papamichail topped Bulgarian Isabella Shinikova 3-6, 6-4, 6-1.

In Group B, contested in Brisbane, Switzerland’s Belinda Bencic and Marc-Andrea Husler defeated their opponents, Yulia Putintseva and Timofey Skatov of
Kazakhstan. Bencic was a 7-6 (0), 6-3 victor, while Husler won 4-6, 6-3, 6-3.

Americans Taylor Fritz and Madison Keys swept their matches to put the U.S. atop Group C in Sydney. Fritz topped Czech Jiri Lehecka 6-3, 6-4, while Keys put away Marie Bouzkova 6-4, 6-3.

And in an upset, the British team of Cameron Norrie and Katie Swan beat the home-crowd favorite Australians, Alex de Minaur and Zoe Hives, each in straight sets in Group D in Sydney. Norrie won 6-4, 6-3, and Hives posted a 6-3, 6-3 match.

In Group F in Perth, the French squad of Alize Cornet and Arthur Rinderknech made quick work of the Argentine duo of Maria Lourdes Carle and Francisco Cerundolo. Cornet won 6-2, 6-1, with Rinderknech gaining a 6-4, 6-2 victory.

The only group that saw a split on Thursday was Group E, played in Brisbane, where Italy and Brazil each won a match. Brazil’s Beatriz Haddad Maia defeated Martina Trevisan 6-2, 6-0, and Italian Lorenzo Musetti bested Felipe Meligeni Alves 6-3 6-4.

Play continues Friday with the same country pairings competing in men’s and women’s singles matches, as well as mixed doubles.

–Field Level Media