Top seed Serena Williams and her older sister Venus led a foursome of American women into the Australian Open fourth round on Saturday.
It is the first time four women from the traditional tennis powerhouse, which has relied on the Williams sisters for much of their Grand Slam success in the past decade, have made the last 16 at a major since Roland Garros in 2013.
The sisters were joined in the last 16 by the two Madisons -- Brengle and Keys -- who will play each other -- with the 19-year-old Keys upsetting twice Wimbledon champion Petra Kvitova 6-4, 7-5 in the last match of the day.
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Serena roared through the rest of the match
While Victoria Azarenka continues to lurk as a danger to anyone in the top half of the draw, an ominous portent developed over the rest of the women's field with the Williams sisters’ success.
The last time the siblings reached the last 16 at Melbourne Park, Serena went on to win her fifth Australian Open title.
It was also the last time the 18-times Grand Slam winner lifted the Daphne Akhurst Memorial Cup.
The World No 1 beat Ukraine's Elina Svitolina 4-6, 6-2, 6-0, while 18th seed Venus also needed a set to get going before she beat Italy's Camila Giorgi 4-6, 7-6(3), 6-1 to make her first Grand Slam fourth round since Wimbledon in 2011.
'It was a good match and she really made me work really hard'
The younger Williams sister took the loss of her first set at Melbourne Park this year to heart and roared through the rest of the match in just over an hour to end Svitolina's hopes of becoming the first Ukrainian woman to reach the fourth round at the Australian Open since Alona Bondarenko in 2010.
"She played really well," Serena said of Svitolina.
"She is one to watch. She has come a really long way. It was a good match and she really made me work really hard."
While Serena was recovering on Rod Laver Arena, older sister Venus was wrapping up her win over the tricky Giorgi to move into a grand slam fourth round for the first time since Wimbledon in 2011.
'This little cat has a few tricks up her sleeve'
"That feels fantastic especially when things happen in your life that are not in your control," said Venus, who struggles with Sjogren's syndrome, an auto-immune disease that can cause joint pain and fatigue.
"But I don't want to stop now, I want to keep it going.
"This little cat has a few tricks up her sleeve."
The 34-year old will now meet women's sixth seed Agnieszka Radwanska who also continued her largely untroubled progress with a 6-0, 7-5 win over another American Varvara Lepchenko, while Serena will play the enigmatic Garbine Muguruza.
The hard-hitting Spaniard beat Serena last year in the second round at Roland Garros and the tall right hander said that victory, while a 'perfect game', was not a factor on the Melbourne hard courts.
"I think I don't have nothing to lose," the 21-year-old said. "Just another match, same game, same concentration.
"Nothing new. ... I don't think I have pressure."
‘It’s going to be another good match’
Women's sixth seed Agnieszka Radwanska also continued her largely untroubled, yet under the radar, progress through the draw with a 6-0, 7-5 win over Varvara Lepchenko and will meet Venus on Monday.
"I think playing her is always great challenge," Radwanska said.
"I think she is still playing great tennis even she's a bit older. She's still really fit and playing a high level.
"I think it's going to be another good match."
Nishikori drops first set tiebreak before beating American Johnson
With Roger Federer's surprise exit on Friday still hanging over the tournament, the men's favourites had some nervous moments in their third round clashes on Saturday.
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Djokovic was forced into a first set tiebreak by former top-10 player Verdasco, while fifth seed Kei Nishikori also dropped the first set tiebreak before he beat Steve Johnson.
Johnson and 19th-seed John Isner, who was beaten by Luxembourg's Gilles Muller, were the last American men in the singles competition, though North America will be represented in the fourth round by Canada's Milos Raonic.
