Madison Keys through as Mattek-Sands retires. Apia Internacional Sydney 2014.

Keys, 18, reached her second career semifinal after her 2013 run at the Osaka tournament where she lost to eventual winner Sam Stosur. Mattek-Sands received treatment on her injury at the 2-1 changeover but at the next change of ends called time on the match when trailing 3-2. “I’ve been through my share of injuries. Once you start compensating too much on the court other things start hurting,” Mattek-Sands said. “For me, I want to take care of my body. It’s not even just about Australian Open, it’s about the rest of my year. My biggest goal is to stay healthy. “I’m a huge competitor and it always hurts to have to withdraw, but I wish the best to Madison.” Keys will play the winner of the quarterfinal between Angelique Kerber and Carla Suarez Navarro, which is just starting on Ken Rosewall Arena. “Bethanie and I always have great matches. It’s always kind of not great when you can’t finish a whole match,” Keys said. “I just hope she’s better for next week.”