Withdrawal sees Federer through
Top seed Roger Federer began his bid to regain the ATP Basel title with a victory after opponent Alexandr Dolgopolov was forced to retire.
With the score at 6-4 5-2, world number two Federer was serving for the match when 21-year-old Ukrainian Dolgopolov turned his right ankle as he stretched to reach a drop shot at the net.
Federer is looking to regain the title in his hometown after losing in last year's final to Novak Djokovic, having claimed the crown in each of the three preceding years.
The Swiss took the initiative midway through the opening set when he converted the first of three break points with a deft drop shot to go 4-3 up.
Dolgopolov, in his first full season on the ATP Tour, had impressed on his serve through much of the first set, but got off to a poor start in the second when a double fault conceded a break point before a wayward forehand gave Federer an early advantage.
The world number 48 then repeated the sequence to put Federer 5-2 up, before his unfortunate injury forced his withdrawal.
France's Michael Llodra came from a set down to beat American John Isner in the final match of the evening.
Llodra lost the first set 6-4, but fought back to take the next two sets 7-5 6-3, and will now face the Netherlands' Robin Haase, who beat home competitor Stephane Bohli 6-4 6-3 in the opening match of the tournament.