Novak Djokovic extended his winning streak to 27 matches and stayed on track for a fourth consecutive Australian Open title with a 6-3, 6-3, 7-5 win Friday over Denis Istomin.

Djokovic, whose last defeat came against Rafael Nadal in the U.S. Open final, is aiming to be the first player to win four Australian Open titles in a row in the Open Era.

Before rain cooled things off at Melbourne Park, Serena Williams persevered through a fourth day of searing temperatures to also advance.

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