MELBOURNE (AFP) - Rafael Nadal and Serena Williams stayed on track at the Australian Open Monday but Andy Murray's campaign came shuddering to a halt and a raft of withdrawals blighted the race to the quarter-finals. Top seed Nadal maintained his perfect record by sweeping past Chile's Fernando Gonzalez and into a last-eight clash with France's Gilles Simon as the Spaniard seeks his maiden hard-court Grand Slam. But pre-tournament favourite Murray went down in a gripping five-setter to Spanish star Fernando Verdasco, who beat the Briton 2-6, 6-1, 1-6, 6-3, 6-4. Rounding out the men's quarter-finals was French fifth seed Jo-Wilfried Tsonga who proved too hot to handle for American James Blake in a 6-4, 6-4, 7-6 (7/3) rout. He will meet Verdasco for a place in the semis. Williams was fortunate in a tournament throwing up plenty of surprises when a distraught Victoria Azarenka retired with an apparent virus while leading 6-3, 2-4. Azarenka, the 2005 Australian junior champion from Belarus, had broken Williams twice to win the first set and was down a break in the second when she became distressed on another scorching Melbourne day. The 19-year-old had a medical time-out at 2-3 in the second set but was staggering around the court before she eventually conceded in floods of tears and was helped off by two trainers. "I woke up at 6:00 am and I was throwing up all morning and just felt weak," she said. "It's very disappointing for me that I played that well and I couldn't handle a little bit more because it was really close games - could have been up 2-0 in the second." Williams was sympathetic. "I feel so bad, she was playing so well," she said. "She can't risk it so I hope she did the right thing. Obviously she was playing really well and she has so many Australian Opens ahead of her." Williams now plays eighth seed Svetlana Kuznetsova, with the Russian also benefiting from a retirement when China's Zheng Jie pulled out with a wrist injury while losing 4-1. "I feel sorry for her because she was in great shape, she was playing good. This pain I hope is not very dangerous," she said of Zheng, who enjoyed her strongest run yet at the season-opening Grand Slam. Looking ahead to Williams, she added: "It's definitely going to be hard. "But I'm confident in myself, and I just want to play my best and will go there with motivation, just fight with spirit hopefully." Fellow Russian Elena Dementieva set up a quarter-final against unseeded Spaniard Carla Suarez Navarro. Dementieva is on a 14-match winning streak this year, with titles in Auckland and Sydney along the way, and has hardly been troubled, blasting past Slovak 18th seed Dominika Cibulkova 6-2, 6-2. Her next opponent, Suarez Navarro, reached her first Australian Open quarter-finals with a businesslike 6-3, 6-2 win over 21st seed Anabel Medina Garrigues. Nadal, who is yet to drop a set, dominated 2007 finalist Gonzalez 6-3, 6-2, 6-4, with the Wimbledon and French Open champion yet to be challenged here after easy wins in all his matches. "I'm playing well and happy with how I'm playing so far but you never know whether it is going to be enough," he said. It was a different scenario for Murray. The Scottish pre-tournament favourite hasn't been feeling well but refused to make excuses. "If I say that I'm sick and it affected me, I know it's going to be like, 'Well, he's making excuses for losing'," he said. "I don't feel that was the reason why I lost. I definitely did have my chances, and he played too well." Simon went through on a retirement as fellow Frenchman Gael Monfils pulled out with a wrist injury when losing 6-4, 2-6, 6-1. It was not the way Simon wanted to beat his friend and he must now regroup with Nadal waiting in the last eight. "You never want to win like this," he said.