Rafael Nadal of Spain lost his opening match of the season Saturday in the countdown to the defense of his Australian Open title, but women's world No. 1 Iga Swiatek of Poland cruised to victory at the United Cup.

Nadal, who was also below-par at the season-ending he Association of Tennis Professionals (ATP) Finals in November, crashed to 14th-ranked Cameron Norrie of Britain 3-6, 6-3, 6-4 in the mixed-teams tournament in Sydney.

The 22-time Grand Slam champion struggled with his first serve, getting just 58 percent in, which ultimately cost him a first defeat to Norrie in their fifth meeting.

"It's pretty crazy, I never won a set before (against him) so firstly I wanted to do that and I had to stay super patient," Norrie said after the 164 minute battle at a packed Ken Rosewall Arena.

"It was a super physical match and huge to get through that and finally beat him. He's beaten me easy the last few times."

Also in Sydney, former world number two Alexander Zverev slumped to defeat in his first ATP match since tearing ankle ligaments during his French Open semi-final against Nadal in June.

The two-time ATP Finals champion hit eight double faults in losing 6-4, 6-2 to 81st-ranked Jiri Lehecka.

"I was able to show up in crucial moments. All the experience from last year, losing to good players, gave me the confidence to play against a player like him," said Lehecka, aged 21.

Olympic champion Zverev, who has dropped to 12 in the world from a career-high two before his injury, was clearly still struggling.

His German teammate Jule Niemeier then lost to Marie Bouzkova 6-2, 7-5 to give the Czech Republic a 2-0 lead in the tie.

In Brisbane, Swiatek got Poland off to the perfect start with a dominant 6-1, 6-3 win over Kazakhstan's Yulia Putintseva.

She broke three times in the first set and twice in the second to completely overpower her opponent in just 64 minutes.

"I'm pretty happy with my performance. First matches of the season are always rusty so I'm happy that in the important moments I was very composed," Swiatek said.

The United Cup tennis event is a new mixed tournament that is currently co-hosted by Sydney, Brisbane and Perth from December 29, 2022 to January 8, 2023.

18 nations, with each comprising of four men and four women, play in a team competition format.

In the round-robin stage, teams will play five matches per tie: two men's singles, two women's singles and one mixed doubles match.

(With input from AFP)