The United Cup tennis tournament began Friday with Spain playing Brazil and Australia taking on Britain in the higher-profile late match at Perth, Western Australia.

The tournament involving mixed teams from 18 countries is being played in Perth and Sydney, where matches begin on Saturday. Two quarterfinalists will be determined from each of the Perth and Sydney group games with the semifinals and the Jan. 7 final set for Sydney.

The format sees men's and women's singles matches played ahead of mixed doubles, the same used by the highly-successful Hopman Cup that was formerly played in Perth.

No. 1-ranked woman Iga Swiatek is representing Poland and playing in Perth. Top-ranked and defending Australian Open champion Novak Djokovic has arrived to represent Serbia, also in Perth.

Serbia will take on China on Sunday and Czech Republic on Tuesday in the group stage, with Djokovic set to face world No. 58 Zhang Zhizhen and No.31-ranked Jiri Lehecka in his men's singles matches.

Djokovic won three Grand Slam singles titles this year, missing out on only Wimbledon, where he lost to Carlos Alcaraz in the final in five sets. He has won the Australian Open a record 10 times among his record 24 Grand Slam singles titles.

On his arrival in Perth, he reiterated he has no plans to retire.

"I hope it's not (the) last (time), to be honest. I mean I always look forward coming back to Australia," Djokovic said. "I always felt like I played my best tennis over the years (here) and had great support."

Djokovic last visited Perth in 2013 when he played at the Hopman Cup.

"It feels great, it's been a while since I was here last," Djokovic said.

"I remember every single time I played in Perth it was great attendance, people love tennis, people love sport in Australia in general. So I don't expect anything less this time, and I'm sure it's going to be a blast for all of us.