The Serena and Venus show that dominated women's tennis for years returned to the Australian Open on Saturday with an unheralded American teenager joining the evergreen Williams sisters in the last 16.
In a banner day for the Stars and Stripes, top seed Serena advanced despite conceding her first set of the tournament, with Venus also battling through and Florida-based 19-year-old Madison Keys sending fourth seed Petra Kvitova home.
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Serena and Venus, aged 33 and 34 respectively, have 25 Grand Slams between them but will not have it all their own way in a tough half of the draw including comeback queen Victoria Azarenka, a two-time Australian champion.
Sixth seed Agnieszka Radwanska and last year's finalist Dominika Cibulkova also burnished their title credentials with easy wins, while the Lindsay Davenport coached Key provided the only upset.
Serena, chasing her sixth Australian crown, was at a loss to explain why she zoned out for the second time in as many matches against Ukrainian 26th seed Elina Svitolina before storming home 4-6, 6-2, 6-0.
Venus won her last Grand Slam at Wimbledon in 2008 but boasts an 8-0 record in 2015, including a title in Auckland, saying she was not just in Melbourne to make up the numbers.
"I've won big. It's not like I haven't done it before," said the American, who will be out to avenge consecutive losses to Poland's Radwanska in the next round.
Radwanska, a semi-finalist last year, is emerging as the tournament dark horse under the tutelage of her new coach, the legendary Martina Navratilova after downing American Varvara Lepchenko 6-0, 7-5.
The 30th seed became the Pole's third consecutive victim to taste the dreaded 6-0 "bagel", with Radwanska, 25, attributing her success to the tweaks 18-time Slam champion Navratilova has made to her game.
Azarenka sounded a warning after beating Czech 25th seed Barbora Zahlavova Strycova in straight sets to confirm her status as the draw's most dangerous unseeded player.
"I do feel I played better than I was playing two years ago… I think my game evolved," said the 2012 and 2013 champion, who is returning from a horror 2014 when she battled injury and depression.
The former world number one will meet Cibulkova, seeded 11, who has done little since losing last year's decider but appears to be gathering steam again at her favourite Grand Slam venue.
Kvitova, the reigning Wimbledon champion, went down 6-4, 7-5 to Keys, who punished the Czech's misfiring serve for the biggest victory of her career.
