An ill Serena Williams remained on track for her 19th grand slam title at the Australian Open with a 6-2, 6-2 demolition of Dominika Cibulkova.

However, sister Venus was sent spinning out of the tournament, beaten 6-3, 4-6, 6-4 by by teenage compatriot Madison Keys, who overcame the re-occurrence of a thigh injury that forced her out of Wimbledon last year.

Serena hammered down 15 aces, to Cibulkova's one, and belted 31 winners to 13 by the 11th seed to advance to her sixth semi-final at Melbourne Park.

Ominously every other time she made the semi-finals, she went on to win the title.

Meanwhile, the 19-year-old Keys, now coached by former number one Lindsay Davenport, showed her maturity and mental toughness once she settled to overpower Venus and battle through the injury that temporarily derailed her in the second set.

Keys took a medical timeout after that game and returned with strapping around her leg and somehow broke Williams twice to get it back on serve, but was then broken again and Williams served out the set 6-4.

Source: Al Jazeera and agencies