Djokovic's backhand strike zone - almost shoulder height
rUse backhand slice to skid the ball - low and away from your opponent's strike zone
Sam Stosur used backhand slice low to Serena William's backhand in US Open final
Serena pondering Stosur's clever tactics during US Open final
Stosur's heavy topspin serve kicked high to Serena's backhand
Serena Williams and the US Open champion Samantha Stosur chat during the presentation ceremony
Use slice and topsin variations to prevent a powerful hitter from connecting in their preferred strike zone – which ideally is between shoulder and waist height for the receiver