Karen Khachanov is through to his first semi-finals at the Australian Open after Sebastian Korda retired from their match with a wrist injury.Khachanov was the dominating force and was up 7-6(5) 6-3 3-0 when the American called it quits.Korda sustained the injury mid-way through the second set and had his wrist strapped up following a medical timeout.From then on out, it was one way traffic as Korda lost seven games in a row before making the decision to retire to prevent aggravating his wrist.It was a disappointing end to his first ever Grand Slam quarter-final, and it marked the first retirement of the t …