AUCKLAND, New Zealand — Serena Williams and Caroline Wozniacki both advanced to the singles semifinals at the ASB Classic on Friday, then extended their first-time partnership to reach the doubles final.

Williams beat Laura Siegemund 6-4, 6-3 and Wozniacki defeated two-time defending champion Julia Goerges 6-1, 6-4 in the quarterfinals.

Both players will face American opponents in the semifinals on Saturday; Wozniacki will play Jessica Pegula and Williams will play Amanda Anisimova.

Williams and Wozniacki then combined to beat Kristen Flipkens and Alison van Uytvanck 7-6 (9), 6-2 to reach their first doubles final. The pair, close friends, are playing doubles together for the first time in their careers.

Wozniacki will retire after the Australian Open and, with Williams, snatched the last chance of their long careers to play doubles.

Friday's results raise the possibility the pair will meet in the singles final on Sunday, then will have to combine in the doubles final.

“I've done it before with my sister (Venus) and we're still really close so I'm sure me and Caroline will still be super close,” Williams said.

Williams had to overcome a swirling wind on centre court to come from a break down in the second set to beat Siegemund. She was able to step up on crucial points, converting three of her five break points.

Siegemund, who beat American teenager Coco Gauff in the second round, stretched Williams with her variety and placement but couldn't match the 23-time Grand Slam champion's power from the baseline.

"She was an incredibly tricky player and the conditions really didn't help," Williams said. “But, oh my God, it's good to get through that.”

Wozniacki was convincing in her win over Goerges, the 2018 and 2019 champion in Auckland. She dominated the game on serve and gave Goerges few chances to fight her way back into the match.

"I've had so many tough matches against Julia in the past and I knew this one was going to be tough as well," Wozniacki said. "I've been serving well this week so hopefully it can continue."

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