Federer eyeing revenge in showdown with Djokovic

Archrivals squaring off Tuesday at ATP Tour Finals in London

Roger Federer will start his bid for a seventh title at the season-ending ATP World Tour Finals with a revenge mission against Novak Djokovic.

After one of the worst campaigns of his illustrious career, Federer arrives for the prestigious event at London's O2 Arena looking to finish the year on a high note and he has an opportunity to make an immediate impact when he faces world No 2 Djokovic on Tuesday.