Serena Williams has beaten Maria Sharapova for the 18th consecutive time, a 6-4, 6-1 win that advances the defending champion to the semifinals of the Australian Open.

Williams, seeking her seventh title here, broke fifth-seeded Sharapova's serve and clinched an entertaining first set on her fourth set points.

She rolled to a 5-0 lead in the second set before Sharapova held serve.

Williams, who also beat 2008 champion Sharapova in the final here last year, also won the French Open and Wimbledon in 2015 and got within two wins of a calendar-year Grand Slam before losing in the U.S. Open finals.

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The No. 1-ranked Williams twice received medical treatment, at the end of the first set and again after the third game of the second.

It was not immediately apparent what was affecting her.Williams, who improved her career record over Sharapova to 19-2, will play No. 4-seeded Agnieszka Radwanska in the semifinals.