Don't talk about mental things - as slam champions these guys obviously have big mental toughness. Leave the issue of peaking at different times out as well - because we've seen that a post-peak Federer beat an absolute peak Djokovic. What in Federer's GAME allows him to have had a good head-2-head against Djokovic through his career? ie. the serve? The backhand (lol). The slice? Please elaborate.