Azarenka, last year’s Australian Open champion and a winner of this tournament in 2009, made light work of quarter-final opponent Ksenia Pervak, beating the Kazakh player 6-1, 6-0.
Pervak knocked out former World No 1 Caroline Wozniacki in the first round but had no answer to the current rankings leader as she made a rapid exit.
Awaiting Azarenka in the last four is third seed Williams, the reigning Wimbledon and Olympic champion, who is eyeing a fifth Australian Open title later this month.
Williams’ tune-up for Melbourne Park continued with a hard-earned 6-4, 6-3 success against fellow American Sloane Stephens.
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