Serena Williams is into the semi-finals of the Australian Open after thumping 11th seed Dominika Cibulkova on Wednesday afternoon.

Williams, who was reported to have had a coughing fit prior to the match, steamrolled her Slovakian opponent, winning 6-2 6-2 in one hour and four minutes.

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Cibulkova was simply blown away by the power of Williams, who cracked 31 winners and sent down 15 aces in a commanding display.

Her opponent in the semis will be American teen Madison Keys, who proved too strong for Serena’s older sister Venus.

Keys won 6-3 4-6 6-4 in a roller-coaster quarter-final despite suffering a groin injury midway through the all-American showdown.

The 19-year-old took a lengthy injury time-out trailing 1-4 in the second set and looked as though she may not be able to continue.

But Keys emerged to push the veteran 15 years her senior to a third set, won with power and poise.

The unseeded Keys had never before won more than two matches at a major from 10 attempts but now finds herself in the last four at Melbourne Park .

The world No.35 is the lowest ranked player left in the draw, but would have the rest of the field worried after powering 34 winners to Williams’ 10 to march on after one hour and 55 minutes.

– with AAP