LONDON (AFP) - Roger Federer is aiming to complete a century of titles at the ATP Finals but will likely have to find a way past the irrepressible Novak Djokovic, who is looking to round off his astonishing season in style.
The two men, with 34 Grand Slams between them, are the twin titans at the season-ending event at London's O2 arena.
But the tournament, which starts on Sunday, lacks an element of star power without the injured Rafael Nadal and Juan Martin del Potro, both of whom were forced to pull out of the season finale.
Former champion Andy Murray, still making his way back from injury, and defending champion Grigor Dimitrov are other star names missing.
The title is contested by the eight players who have accumulated the most ranking points over the season and is in a round-robin format, with the best four players reaching the knockout semi-finals stage.
Federer is expected to emerge from Group Lleyton Hewitt, also featuring Kevin Anderson, Dominic Thiem and Kei Nishikori, while Djokovic is highly fancied to top Group Guga Kuerten, which also includes Alexander Zverev, Marin Cilic and John Isner.
After a stunning 2017 season which saw the Swiss capture seven titles, including Grand Slam crowns at the Australian Open and Wimbledon, Federer was clear that his 2018 season has been a success despite a mixed run of results in recent months.
Djokovic has made an incredible comeback following elbow surgery early in the year, overcoming indifferent form to win Wimbledon and the U.S. Open and haul himself back to the number one spot.
The 31-year-old, who slipped to 22nd in the world in May, admitted that after his surgery it looked improbable that he would finish the year as number one.
********* Novak Djokovic and Roger Federer (AFP Photo/Anne-Christine POUJOULAT