Dominant Swiatek sends Poland into the United Cup quarter-finals

The world number one showed no mercy to Sara Sorribes Tormo in a 6-2, 6-1 singles victory before teaming with Hubert Hurkacz to clinch the tie with a 6-0, 6-0 mixed doubles thrashing in just 53 minutes.

Hurkacz was ambushed in the day's opening singles, losing 3-6, 6-3, 6-4 to Alejandro Davidovich Fokina.

The top-seeded Poles finished Group A play with a perfect 2-0 record and await a last-eight opponent.

Swiatek, who has lost only seven games in two singles matches to start her countdown to the Australian Open, said playing mixed doubles was good experience.

"It's lessons for the future and great practice," the 22-year-old said. "I hardly ever play mixed. You use different skills, it's about feeling the geometry of the court."

Hurkacz credited his teammate with doing most of the hard yards.

"She carried me throughout the whole match, in every game she was making amazing shots," the world number nine said.

A sharp Casper Ruud won his second straight singles match of the season on Monday before backing up in the mixed doubles to steer Norway past Croatia at the United Cup.

World number 23 Donna Vekic ground past unheralded Malene Helgo 7-5, 3-6, 6-3 to give the Croats a winning start to the Group F tie at the mixed teams tournament in Sydney.

But three-time Grand Slam finalist Ruud swept past Borna Coric 6-4, 6-1 in just 89 minutes to level proceedings, then teamed with Ulrikke Eikeri to beat Vekic and Ivan Dodig 6-2, 3-6, 10-7.

It was a much-needed win for Norway who lost against the Netherlands at the weekend.

"I'm motivated for the new year, I'm fresh and I'm ready," said world number 11 Ruud. "Another great singles match. I'm very happy to start the new year that way."

It followed a similarly dominant 6-3, 6-4 win over Dutchman Tallon Griekspoor on Saturday.

Ruud has dropped serve just once through the two matches, and was not broken on Monday.

He also won 12 of 13 net approaches and said he had been working hard to improve his volleys.

"I'll never be the guy who is all over the net, but I'm trying to come into the court a little more," he said.

Vekic needed two hours and 49 minutes to battle past Helgo, who played far better than her ranking of 539 suggested.

"She's a really good player and her ranking doesn't do her justice," said Vekic, a quarter-finalist at the Australian Open last year.

"Finally my serve showed up in the third set, which made it easier."

Vekic was put to the test in the first set, falling 5-2 behind before winning the next eight points to get back on serve and coming through 7-5.

Helgo took another 5-2 lead in the second set and this time hung. But Vekic broke for a 4-2 advantage in the third and converted her second match point at 5-3 to win.

The Alexander Zverev-led Germany meet France in Group D later Monday in Sydney after beating Italy 2-1 in their opening tie.