A day of contrast for the Williams sisters in Miami only served to highlight Serena's current dominance as the world number one marched into the quarter-finals of the Nasdaq-100 Open while, later in the day, Venus crashed to a shock defeat with her worst result in 13 months.

Venus lost 7-6 (7-2) 6-1 to her compatriot Meghann Shaughnessy, the world number 28, falling away disastrously in the second set in which she made a host of unforced errors. Serena, meanwhile, looked happy to be back at the tournament which launched her on the path to fame. It was in Miami a year ago that she beat Venus and went on to the title, a triumph which propelled her to a sensational run in which she captured all four Grand Slam crowns.

On Monday, Serena, who received her award for winning the WTA Tour Player of the Year for 2002 on court, overcame both Iroda Tulyaganova and the lingering remnants of the virus which had threatened to cause her withdrawal from the event. Serena's 6-0 6-4 success against the former top 20 player from Uzbekistan meant that she has so far dropped only 13 games in six sets.

It augurs well for her quarter-final meeting with the surprise survivor, Marion Bartoli, an 18-year-old French qualifier who came through when former world number one Lindsay Davenport retired after one set with a damaged hamstring.

In the men's event Andre Agassi moved closer to becoming the first player ever to win three titles in a row in Miami when he raced into the men's last 16. Agassi was in outstanding form as he walloped Jarkko Nieminen, the 32nd seeded Finn, for the loss of only two games.

With world numbers one and three Lleyton Hewitt and Juan Carlos Ferrero both out of the tournament, Agassi's chances of a record-breaking hat-trick appear to be improving markedly. Agassi now faces an in-form Mark Philippoussis, who beat the Swedish Davis Cup player Thomas Enqvist 6-7 (6/8) 7-6 (7/3) 6-3.

Filed by Shane Murray