Unlike her earlier sluggish matches, Serena was in the zone from the off against the dangerous Slovak, a steely look in her eyes as she walked onto Rod Laver Arena soon after Venus lost to Keys.

The powerful world number one blasted 15 aces to pummel the 11th seed 6-2 6-2 in just over an hour and make her 26th Grand Slam semi-final. She has gone on to win 18 major titles.

"I knew that I had to beat her today because she was in the final and she plays really well on this court so I'm really happy to go through," said Serena, who has been battling a cold and could barely talk.

Long-time rival Maria Sharapova made the last four yesterday and will face fellow Russian Ekaterina Makarova.

The unseeded Keys, 19, is the tournament surprise package, battling hard to beat a resurgent Venus 6-3 4-6 6-4 and end any chance of the sisters meeting in a Grand Slam semi for the first time since Wimbledon 2000.

Keys did the job despite carrying a left thigh injury, needing a medical timeout in the second set for treatment.

"I think just being able to come back from being down and from not being able to move as well just being able to kind of grind through that, still manage to win some points, is what I'm most happy about," she said.

Among the men, Andy Murray and Tomas Berdych are already safely into a semi-final showdown after beating Nick Kyrgios and Rafael Nadal respectively.

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