MELBOURNE, Australia (AP) — Most things about this week leading into a major are different for Serena Williams.

The 23-time Grand Slam champion got to try something new Friday, too, needing a match tiebreaker to beat fellow American Danielle Collins 6-2, 4-6, 10-6 and set up a semifinal against top-ranked Ash Barty in the Yarra River Classic.

“I felt good to get through that in a tiebreaker," Williams said. “Definitely different."

Even more different is that Williams doesn't usually play in the week before a major.

That's been the theme for this Australian Open, which was delayed three weeks so that all players and their entourages could spend 14 days in hotel quarantine under the strict regulations in place for the COVID-19 pandemic.

A day after all matches in six tournaments were postponed so that 160 players could isolate and undergo testing because a worker at a quarantine hotel returned a positive test, there were 70 matches on the order of play as organizers tried to cram all scheduled lead-in matches into three days. The Australian Open starts Monday.

Barty also got her first taste of the modified scoring system introduced to shorten matches in a disrupted schedule, dominating a match tiebreaker to beat Shelby Rogers 7-5, 2-6, 10-4.

In a reverse of the result of last year's Australian Open final, Garbine Muguruza beat Sofia Kenin 6-2, 6-2 to advance to the semifinals. Kenin beat Muguruza in the 2020 final in three sets, including by 6-2 scores in the final two sets.

Australian Open tournament director Craig Tiley did a radio interview before play started and announced that 507 people with connections to the tournament quarantine hub test had been tested and 495 had already returned negative tests for the coronavirus. He said results for 12 people were pending.

Play was halted as a precaution after a quarantine worker tested positive this week, days after his last shift at the hotel, and all players and tournament-related people at the Grand Hyatt were regarded as casual contacts. State health authorities on Friday said there were no further cases of community transmission in the previous 24 hours..

To speed things up a little, 17 courts were being used and women's matches were reduced to two regular sets with a 10-point match tiebreaker if required.

Barty opened proceedings on Margaret Court Arena and after some up-and-down form in the first two sets, she raced to a 6-1 lead in the match tiebreaker and finished the tiebreaker off in 12 minutes.

“A bit of an unusual scoring system for us," Barty said. “Happy to get through and have another chance tomorrow."

“It’s the challenge, regardless of what conditions you’re dealt with," she said of the situation so close to the year's first major.

AZARENKA ADVANCES

Two-time Australian Open champion Victoria Azarenka beat Yulia Putintseva 6-4, 1-6, 11-9 to advance at the Grampians Trophy, an event staged for the players forced into hard lockdown during quarantine.

Sorana Cirstea upset Belinda Bencic, the highest-ranked player in the tournament, 7-5, 6-2 before a clap of thunder and a rain shower suspended play on outside courts.

SPAIN INTO SEMIS

Pablo Carreno Busta clinched Spain a spot in the ATP Cup semifinals with a 6-3, 6-4 win over Michail Pervolarakis in the opening singles match against Greece. The win ensured Spain had enough points to top Group B, which also includes Australia.

No. 2-ranked Rafael Nadal was skipping the encounter against Greece to give his sore back more time to rest, leaving No. 16-ranked Carreno Busta and No. 13-ranked Roberto Bautista Agut again to fill the singles spots.

“I knew we needed this point," Carreno Busta said in his on-court interview. “With this victory, we are into the semifinals, so it was very important to us.”

Greece rallied for 2-1 win over Spain, with Stefanos Tsitsipas beating Roberto Bautista 7-5, 7-5 and then combining with Pervolarakis in the deciding doubles match — which lasted only one game before the Spanish pair retired.

In other ATP Cup matches, defending champion Serbia and Germany were 1-1 after Novak Djokovic edged Alexander Zverev in the second singles match. The winner of the doubles will finish atop Group A and reach the semifinals.

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