This is the second edition of the United Cup, but Sunday’s searing Day 3 lineup delivers a startling variety of firsts.

On the last day of 2023, four nations -- Canada, Chile, China and Serbia -- make their United Cup debut. And, against the odds, all three marquee Hologic WTA Tour singles matches are never-happened-before encounters.

Defending champion Team USA and Great Britain, two returning teams from a year ago, face off in Perth in a critical Group C matchup, followed by China versus the Novak Djokovic-led Serbia squad. In Sydney, it’s Canada versus Chile. 

Hold on to your hats, for you’re about to witness a series of things that have never, ever happened.

The heat is on in Perth

It’s summer in Western Australia and temperatures have been reaching into the high 90s. Inside at RAC Arena, it’s likely to be even hotter.

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One of Jessica Pegula’s first observations after touching down in Western Australia was how difficult it would be for the United States to repeat. She cited the new best-of-three format, which places less of a premium on depth than last year’s best-of-five. She also mentioned Group C’s talented rosters.

For Jessica Pegula, United Cup served as springboard for another stellar season

Speaking of which, Great Britain is already 1-0, after Friday’s 2-1 victory over Australia. Katie Boulter was an emphatic 6-2, 6-4 winner over Ajla Tomljanovic. Cameron Norrie was a three-set winner over Alex de Minaur. Boulter, 27, had a breakthrough season in 2023, jumping nearly 50 spots in the rankings by winning her first title last summer in Nottingham.

“Four or five years ago, I was ranked No.80 and unfortunately I had a massive [back stress fracture] injury,” Boulter told WTAtennis.com. “It took me a long time to come back from that. Last year was the first one where I wasn’t injured at some point in the year in my career. For me, it was a huge stepping stone.

“I’ve got a lot coming in from 2023. And I’ve put a lot of work in, but I’m not expecting to win every single match. For me, it’s about day-to-day improvement, focus on the process, making sure I’m really ready every single day. I really hope I can push on and make some gains coming up.”

Ranked No.56, Boulter will take on No.5 Pegula, who won four of five United Cup singles matches a year ago.

Later, China’s Zheng Qinwen (No.15) meets Olga Danilovic (No.119) of Serbia. Zheng defeated Wimbledon champion Marketa Vondrousova 6-1, 2-6, 6-1 on Saturday to clinch China's 3-0 win over the Czech Republic.

Zheng Qinwen overcomes Vondrousova in United Cup group play

Last year, Zheng finished with a flourish, winning the title in Zhengzhou and reaching the finals of the WTA Elite Trophy in Zhuhai to raise her ranking to a career-high No.15.

“I’m so happy to have won all those tournaments in China, especially in front of all my people,” Zheng said after her opening win. “But actually, I feel it's come a little bit slow, because I remember at the beginning of 2023 I say I will make Top 10. I really think that I can do much better than that.

“So right now I just keep telling myself the target is there, but I need to watch my steps and take good every single step and live in the moment.”

Play begins at 10:00 a.m.

Group C: USA (0-0) vs. Great Britain (1-0)

Jessica Pegula (USA) vs. Katie Boulter (GB)
Taylor Fritz (USA) vs. Cameron Norrie (GB)
Followed by mixed doubles

Group E: China (1-0) vs. Serbia (0-0)

Zhang Zhizhen (China) vs. Novak Djokovic (Serbia)
Zheng Qinwen (China) vs. Olga Danilovic (Serbia)
Followed by mixed doubles

Meanwhile, in Sydney …

While Iga Swiatek won her last 11 matches of 2023 to recapture the No.1 ranking, Leylah Fernandez was right behind her.

The 21-year-old Canadian won 11 of her last 12 in a little over one month -- sweeping to the title in Hong Kong, reaching the semifinals in Nanchang and going 2-0 to help Canada to the Billie Jean King Cup title.

It was a fantastic finish for the player who struggled after reaching the 2021 US Open final. Now she'll try to lead Canada to another team title.

“I get to ask some advice from my team members, have some good time on court,” Fernandez told reporters. “I think also I’ll learn from them. It’s not just going to be me and myself in this tournament. I get to share the wins and the losses with them. We get to pump ourselves up even more. I just know that it's going to be an amazing experience.”

The No.35-ranked will be a heavy favorite over No. 668 Daniela Seguel of Chile.

Play begins at 10:30 a.m.

Group B: Canada (0-0) vs. Chile (0-0)

Leylah Fernandez (Canada) vs. Daniela Seguel (Chile)
Steven Diez (Canada) vs. Nicolas Jarry (Chile)
Followed by mixed doubles