MELBOURNE, Australia (AP) Serena Williams loves having Venus back to keep her company in the second week of a Grand Slam, and credits her older sister with giving her the motivation to reach the fourth round of the Australian Open.
The Williams siblings, with 25 Grand Slam titles between them, will have a couple of Madisons joining them, too.
Madison Keys had a 6-4, 7-5 upset win over two-time Wimbledon champion Petra Kvitova on Saturday night, and Madison Brengle beat Coco Vandeweghe 6-3, 6-2 in an all-U.S. third-round match. The two Madisons will meet in the round of 16, meaning one of them will become a first-time Grand Slam quarterfinalist.
The last time four or more American women reached the second week in Australia was in 2003, when Keys' coach Lindsay Davenport was playing and Serena beat Venus in one of their Williams-sister finals. That can't happen this time, because they're in the same half of the draw.
Serena Williams, who is aiming for her sixth Australian and 19th Grand Slam title, has long been the standard bearer and has been asked all too often what has happened to the depth of U.S. women's tennis.
''I think American women's tennis has come so far. We have so many options now, which is so great because for years I had to answer the question: `I don't know, I don't know,''' the No. 1-ranked Williams said after her 4-6, 6-2, 6-0 win over No. 26-ranked Elina Svitolina. ''Just so many American players that are playing really, really well. So much to look forward to.''
None more, in her mind, than Venus' return to the fourth round at a major for the first time since Wimbledon in 2011.
When Serena walked onto Rod Laver Arena on Saturday, Venus was down a set and a break on nearby Margaret Court Arena. Venus, who was diagnosed with an auto-immune condition called Sjogren's syndrome in 2011 and has struggled at the highest level ever since, rallied for a 4-6, 7-6 (3), 6-1 win over Camila Giorgi. And that was powerful inspiration.
''I thought, `Wow, she's been through so much with her illness, with everything that she's had to do. Gosh, if she can do it, I'm perfectly healthy, I'm fine. I should be able to do it, too,''' Serena Williams said.
On the men's side, top-ranked Novak Djokovic and defending champion Stan Wawrinka advanced with straight-set wins, while U.S. Open finalist Kei Nishikori and Wimbledon semifinalist Milos Raonic continued their quests for a first major title.
Four-time Australian Open winner Djokovic beat Fernando Verdasco 7-6 (8), 6-3, 6-4 in the first night match on Rod Laver, then asked the crowd of 15,000 to help him sing Happy Birthday to his mother, Dijana.
''It's my mom's birthday, can you sing happy birthday?'' he asked the crowd. He sang the whole song live on camera and then left the court to start preparing for a match against Gilles Muller, who beat No. 19 John Isner 7-6 (4), 7-6 (6), 6-4.
Wawrinka had a 6-4, 6-2, 6-4 win over Jarkko Nieminen and will have a score to settle in the next round against Guillermo Garcia-Lopez, who beat him in the first round of the French Open last year.
No. 5 Nishikori beat Steve Johnson 6-7 (7), 6-1, 6-2, 6-3 and will next meet former French Open finalist David Ferrer, who struggled to finish off No. 18 Gilles Simon in four sets. No. 8 Raonic fired 22 aces in a 6-4, 6-3, 6-3 win over Benjamin Becker and will next play No. 12 Feliciano Lopez.
Serena Williams will have to be top of her game when she meets No. 24 Garbine Muguruza, who beat her in the second round at the French Open last year.
In the other fourth-round match in that quarter, two-time champion Victoria Azarenka will meet 2014 finalist Dominika Cibulkova.
Azarenka, who is unseeded because of an injury-interrupted 2014, had a 6-4, 6-4 win over No. 25 Barbora Zahlavova Strycova, while Cibulkova beat No. 19 Alize Cornet 7-5, 6-2.
Venus Williams was delighted after her win, beaming a smile as she turned to wave to all sides of the stadium and doing some dance moves to the loud music. She said Serena had helped her, too.
''We've had the fortunate relationship to be able to motivate each other and grow from each other,'' she said.
The 34-year-old, seven-time major winner is determined to make sure her run doesn't end in the next round against sixth-seeded Agnieszka Radwanska.
''I like to win titles ... that's what I play for,'' she said.