Serbia's Novak Djokovic dropped a set to France's Enzo Couacaud, but the fourth seed progressed to the third round of the Australian Open ©Getty Images

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Nine-time winner Djokovic struggled with an existing hamstring injury, and had to take a medical timeout during the match ©Getty Images
Nine-time winner Djokovic struggled with an existing hamstring injury, and had to take a medical timeout during the match ©Getty Images
Norway's world number three Casper Ruud, right, was the highest-ranked men's singles casualty of the day, losing to American Jenson Brooksby, left ©Getty Images
Norway's world number three Casper Ruud, right, was the highest-ranked men's singles casualty of the day, losing to American Jenson Brooksby, left ©Getty Images
Two-time Olympic champion Sir Andy Murray of Britain played the longest match of his career, his epic comeback victory against Australia's Thanasi Kokkinakis finishing at 4.05am local time ©Getty Images
Two-time Olympic champion Sir Andy Murray of Britain played the longest match of his career, his epic comeback victory against Australia's Thanasi Kokkinakis finishing at 4.05am local time ©Getty Images
Women's singles second seed Ons Jabeur of Tunisia lost to Czech Republic's Olympic silver medallist Markéta Vondroušová at the second round stage ©Getty Images
Women's singles second seed Ons Jabeur of Tunisia lost to Czech Republic's Olympic silver medallist Markéta Vondroušová at the second round stage ©Getty Images
Caroline Garcia of France overcame Canada's Leylah Fernandez 7-6, 7-5 to reach the third round ©Getty Images
Caroline Garcia of France overcame Canada's Leylah Fernandez 7-6, 7-5 to reach the third round ©Getty Images
Belarusian Aryna Sabalenka, playing as a neutral, eased through against the United States' Shelby Rogers ©Getty Images
Belarusian Aryna Sabalenka, playing as a neutral, eased through against the United States' Shelby Rogers ©Getty Images
Rogers was overpowered by fifth seed Sabelenka in their match at Melbourne Park ©Getty Images
Rogers was overpowered by fifth seed Sabelenka in their match at Melbourne Park ©Getty Images
Swiss Olympic champion Belinda Bencic saw off American Claire Liu 7-6, 6-3 ©Getty Images
Swiss Olympic champion Belinda Bencic saw off American Claire Liu 7-6, 6-3 ©Getty Images
Former world number two Anett Kontaveit of Estonia, left, lost to Poland's Magda Linette, right, 3-6, 6-3, 6-4 ©Getty Images
Former world number two Anett Kontaveit of Estonia, left, lost to Poland's Magda Linette, right, 3-6, 6-3, 6-4 ©Getty Images