Laura Siegemund retired from her Olympic singles first round match with an ankle problem on Sunday, a precaution so she can focus on the doubles with retirement-bound Angelique Kerber and the mixed doubles with 2021 men’s gold medallist Alexander Zverev. Siegemund took a medical timeout over the left ankle problem and then decided not to play on against American Danielle Collins, who was leading 6-3, 2-0 at the time. “I have had problems with the ankle for a while,” Siegemund said, adding that the doubles and mixed have “absolute priority.” While Siegemund was not considered a medal contender …