The ATP and WTA tours' new joint venture begins on Thursday in three Australian cities with plenty of prize money and ranking points at stake. (More Tennis News)

And the mixed teams United Cup could also help shake off some of the holiday season rust ahead of the Australian Open starting Jan. 16 in Melbourne.

The inaugural United Cup has teams from 18 countries competing in Brisbane, Perth and Sydney through to Jan. 4. Then the three city champions and the next-best performing country from the group stage will meet at Ken Rosewall Arena in Sydney from Jan. 6 to 8 to determine the overall winner.

The tournament offers $15 million in prize money and up to 500 ATP and 500 WTA rankings points.

Despite not playing Davis Cup for Australia recently, Wimbledon finalist Nick Kyrgios will lead the host country.

“Obviously being home, but being able to play in Sydney, in front of the home fans, my family, my friends, there's nothing more that I love,” Kyrgios said.

Australia will begin group play against Britain in Sydney on Thursday, with Kyrgios taking on Cameron Norrie. He'll then face Rafael Nadal on Jan. 2 when Australia takes on Spain.

“To be honest I've never really played that great in Sydney, but I'm hoping I'm going to change that narrative at the start of the year,” Kyrgios said. “Just playing in Australia in general is special. The tour is a long grind and it's rarely in Australia, so I'm definitely not going to take it for granted.”

Top-seeded Greece is led by world No. 3 Stefanos Tsitsipas and No. 6-ranked woman Maria Sakkari. World No. 1 Iga Swiatek and No. 11 Hubert Hurkacz will lead second-seeded Poland, with third-seeded United States featuring world No. 3 Jessica Pegula, ninth-ranked Taylor Fritz, world No. 11 Madison Keys and No. 19 Frances Tiafoe.

Nadal will team with world No. 13 Paula Badosa for Spain, while Italy will have world No.16 Matteo Berrettini and Martina Trevisan.

Each host city will feature two groups of three countries, competing in a round-robin format. Each tie will have two men and two women's singles matches and one mixed doubles match to be played over two days.

Among other matches on Thursday's opening day, the United States plays Czech Republic in a day Group C encounter, also in Sydney. In Brisbane, it's Italy vs. Brazil in a day Group E match and Switzerland vs. Kazakhstan at night in Group B.

At Perth, Greece plays Bulgaria in Group A and France plays Argentina later in a night Group F match.