Top seed Serena Williams advanced to the quarter-finals of the Miami Open as Venus Williams upset fourth seed Caroline Wozniacki.
Serena beat 24th seed Svetlana Kuznetsova 6-2 6-3, while her elder sister Venus, who is the 16th seed, beat former world number one Wozniacki of Denmark 6-3 7-6 (7/1).
Venus will play Carla Suarez Navarro, the 12th seed, in the last eight after the Spaniard saw off seventh seed Agnieszka Radwanska of Poland 5-7 6-0 6-4.
Next up for Serena is a clash with Sabine Lisicki of Germany after her 6-1 6-2 defeat of Italy's Sara Errani.
Serena Williams overcame a spirited challenge from fellow American Madison Keys to become the oldest Australian Open finalist in the open era on Thursday.
Williams recovered from a break down in the opening set and saw teenager Keys save seven match points before eventually securing a 7-6 (7/5) 6-2 win in an hour and 24 minutes on Rod Laver Arena.
The world number one will face second seed Maria Sharapova in Saturday's final after Sharapova had earlier defeated fellow Russian Ekaterina Makarova in straight sets.
Caroline Wozniacki has congratulated Serena Williams on her 18th Grand Slam title, saying, "Unfortunately I lost to a better player".
The Danish tennis star wrote on Twitter.
Serena Williams struggled to hold back the tears as she explained the "wonderful feeling" of winning a sixth US Open title 15 years after her first.
As Williams collected a cheque for $4 million (£2.5 million), the biggest in tennis history, she said: "It was a wonderful finish, I couldn't have thought of any better way.
"Congratulations to Caroline [Wozniacki], she's known what a struggle it's been for me, we text almost every day.
"I know you're going to win [a Grand Slam) very soon, maybe even in Australia. I've got to go home and get fit again so I can get ready for you."
Serena Williams has won her third consecutive US Open women's championship after defeating Denmark's Caroline Wozniacki 6-3, 6-3.
The Grand Slam title was the 18th of Williams' career but the American's first of this year.
Serena Williams was forced to pull out of her doubles match with sister Venus at Wimbledon after she became unwell on court.
In scenes which were often uncomfortable to watch, the American appeared dizzy on court and was unable to hit or bounce the ball.
After she served four consecutive double faults, umpire Kader Nouni came down to speak to the sisters as the worrying situation continued.
The sisters eventually forfeited the match against German Kristina Barrois and Swiss Stefanie Voegele after going 3-0 down in the first set.
The commentator said Williams, who has won five Wimbledon singles titles, was a "shadow of herself" and appeared to be "sleepwalking" through the match.
Defending Wimbledon champion Serena Williams has been knocked out of Wimbledon by German Sabine Lisicki.
Lisicki won 6-2 1-6 6-4 to set up a quarter final clash with Kaia Kanepi who defeated British hopeful Laura Robson earlier today.
Williams's exit follows a host of shock exits last week with top seeds Roger Federer, Rafael Nadal and Maria Sharapova all going out.
Serena Williams launched a charm offensive as she sought to broker a truce with Maria Sharapova and calm the storm surrounding comments she made about a rape victim.
The focus of the pre-Wimbledon press conference was about the interview she gave to Rolling Stone magazine that touched on a high-profile teenage rape case in Ohio and brought her into conflict with her Russian rival Sharapova.
The defending champion said she personally apologised to Sharapova and told her she was "very sorry for this whole situation":