Adelaide: Angelique Kerber's preparations for the opening Grand Slam of the year were dealt a blow Wednesday when she was forced to retire from the Adelaide International with back pain. The German former world number one, who won the Australian Open in 2016, pulled out when behind 6-3, 2-0 in her second-round clash with Ukraine's Dayana Yastremska. The ninth seed began showing serious signs of the back problem early in the second set then stopped after two points in the third game on her own serve, calling for the trainer.

A medical evaluation on court ended with the 31-year-old world number 18 calling it quits against her teenaged opponent. Yastremska kept calm during the delay, reading what she called "secret" notes. "I didn't want to lose focus," said the world number 24, who has won three titles over the past two seasons. Men's second seed Felix Auger-Aliassime converted on the first of six match points, firing a service winner to complete a 6-3, 7-6 (7/0) defeat of Australian James Duckworth.