Melbourne: A fired-up Serena Williams shot down last year's finalist Dominika Cibulkova Wednesday to set up an all-American Australian Open semi-final with teenager Madison Keys, who brought sister Venus' dream run to a grinding halt.

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.