MELBOURNE: Top seed Serena Williams and her older sister Venus led a foursome of American women into the Australian Open fourth round on Saturday, while men’s top seed Novak Djokovic survived a nervous start to overcome a feisty Fernando Verdasco.

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 and Brengle beating Coco Vandeweghe 6-3, 6-2 in an all-US match.

“I think my hands are still shaking,” said Keys, who is coached by former number one Lindsay Davenport. “I’m excited to play Maddie in the next round.”

Twice champion Victoria Azarenka also advanced after a 6-4, 6-4 victory over 25th seed Barbora Zahlavova Strycova and will now meet last year’s beaten finalist Dominika Cibulkova who beat 19th-seeded Alize Cornet 7-5, 6-2.

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.