Former champion Angelique Kerber made an early exit from the Australian Open and said spending two weeks in hard quarantine ahead of the grand slam had contributed to her first-round loss. Serena Williams showed no signs of a shoulder injury as she strolled through with a commanding win over German Laura Siegemund, while Japanese third seed Naomi Osaka was the first big gun to register a win on day one at Melbourne Park. Kerber, the German former world No 1, was one of 72 players