World No. 1 Iga Swiatek led Poland into the quarter finals of the United Cup mixed teams tennis tournament on Monday, winning both her singles and doubles matches.

Swiatek took the court under pressure, needing to win her singles match against Spain's Sara Sorribes Tormo to keep the tie alive. Alejandro Davidovich Fokina had given Spain a 1-0 lead with a 3-6, 6-3, 6-4 comeback victory over world No. 9 Hubert Hurkacz.

But Swiatek beat Sorribes Tormo 6-2, 6-1 to force a deciding mixed doubles match. Swiatek, a four-time grand slam singles champion, and Hurkacz then needed little more than half an hour to wrap up the tie with a 6-0, 6-0 win to make Poland the first country through to the quarter finals.

In Sydney, three-time grand slam singles finalist Casper Ruud kept Norway's quarter final chances alive with similar victories in the singles and mixed doubles against Croatia.

Donna Vekic gave Croatia an early 1-0 lead with a 7-5, 3-6, 6-3 win over unheralded Malene Helgo. But Ruud then beat Borna Coric 6-4, 6-1 to send the tie to a decisive mixed encounter, which Norway claimed in a match tiebreaker.

The 6-2, 3-6, 10-7 victory for Ruud and Ulrikke Eikeri over Vekic and Ivan Dodig leaves Norway (1-1) awaiting the outcome of the last remaining Group F match between Croatia (0-1) and the Netherlands (1-0) on Tuesday.

Novak sails

Novak Djokovic closed out his spectacular 2023 on a winning note as the world No.1 eased past China's Zhang Zhizhen 6-3, 6-2 on his United Cup debut on Sunday before doubling up to secure a 2-1 victory for Serbia in the mixed team tournament.

The 36-year-old showed no signs of slowing down as he lifted the Australian, French and US Open trophies last season — with his only blip being a five-set defeat in the Wimbledon final — before securing the year-end top spot at the ATP Finals.

Djokovic wasted little time in priming himself for a tilt at a record-extending 11th trophy at the Australian Open as he dismantled world No. 58 Zhang in 72 minutes at a packed RAC Arena in his first match of the 2024 season.

Djokovic needed just 74 minutes to beat Zhang as he converted three of the seven break points.

Zheng Qinwen rolled over Olga Danilovic 6-4, 6-2 to make it 1-1 but Djokovic returned to partner Danilovic and seal a 6-4 1-6 10-6 victory against Zheng and Zhang.

“It's great to be back in Perth,” Djokovic said afterward. “It's been 10 years since I've been in Perth, and this arena is definitely one of the nicest, from inside and outside, that I've played in.”

Djokovic said he felt a bit rusty early against Zhang and a “little bit out of rhythm” because of not playing a match for over a month.

“It obviously takes a little bit of time to get the engines going and he was serving well,” he said. “I think the serve was great on my part, whenever I needed to get myself out of trouble, at 15-15 or 30-30 in my service games, I found a good serve."

Taylor Fritz and Jessica Pegula combined to help the United States beat Britain 2-1 in Group C.