By Matt Smith DUBAI (Reuters) – Novak Djokovic and Roger Federer renew their great rivalry when they meet in the final of the Dubai Championships on Saturday with both players fighting fit and ready for battle. A few months ago they were had been supposed to bring the curtain down on the ATP Tour with a blockbuster at London's O2 Arena, only for Federer to withdraw injured. They have 10 Dubai titles between them and while Federer leads 19-17 in head-to-heads, Djokovic prevailed in the one that really mattered last year to win the Wimbledon title. "When you play Roger, it's always a great challenge," Djokovic, 27, told reporters after beating fourth seed Czech Tomas Berdych 6-0 5-7 6-4 in Friday's semi-final.