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 in September, is aiming to be the first player to win four Australian Open titles in a row in the Open Era. He has won all three matches so far in straight sets and his major threats - top-seeded Nadal, Wimbledon champion Andy Murray and 17-time Grand Slam singles champion Roger Federer - are in the other half of the draw. Having the right approach to the court, having the right intensity, starting from the first point to try to show to your opponent that you're there to win.'' Before rain cooled things off at Melbourne Park, Serena Williams persevered through a fourth day of searing temperatures to also advance. More...