Andy Murray, Scotland, No. 1 – Murray has the highest win percentage on the tour this year and, having followed in the footsteps of Tim Henman (2003) and Greg Rudedski (1998) with victory at the Paris Masters earlier in November, he's now attempting to become the first Brit in history to win the ATP World Tour Finals. A "Group of Death" stands in his way -- with world No.3 Stan Wawrinka having won seven of his 16 matches against Murray in his career. But, in the midst of a 19-match winning streak, Murray won't want to concede the world No.1 spot any time soon.
• Titles in 2016: 8 - Wimbledon, Olympics, Queen's Club, Paris Masters, Rome Masters, China Open, Shanghai Masters, Vienna Open
• Aces in 2016: 527
• Win percentage in 2016: 89% -- highest of the eight contenders
Kei Nishikori, Japan, No. 5 – The highest-ranked Asian player in ATP history, Kei Nishikori captured a fourth straight title at the Memphis Open in February before going on to win Olympic singles bronze in Rio, beating Nadal in three sets. Nishikori, 26, is the first Japanese singles medalist since Ichiya Kumagae at Antwerp 1920.
• Titles in 2016: 1 - Memphis Open
• Aces in 2016: 245
• Win percentage in 2016: 76%
Marin Cilic, Croatia, No. 7 – Standing at 198cm, Cilic is the tallest of the ATP finalists and a full 20cm taller than opponent Nishikori. He reached a third consecutive Wimbledon quarterfinal in 2016, but lost out to Roger Federer despite leading by two sets and holding three match points. Capping a resurgent end to 2016, Cilic has led Croatia to the Davis Cup final with wins over Belgium, USA and France, and will take to the court against Del Potro's Argentina later in November. Murray partly has Cilic to thank for his No. 1 berth -- he upset Djokovic with a supreme display of power tennis in the Paris Masters quarterfinal, beating the Serbian for the first time in his 15th attempt.
• Titles in 2016: 2 Cincinnati Masters, Swiss Indoors Basel
• Aces in 2016: 636
• Win percentage in 2016: 69%
Novak Djokovic, Serbia, No. 2 – Djokovic became just the third man in history to hold all four majors at once when he won the French Open in June, and the first player to surpass $100 million in prize money. For now, his throne has been seized by Murray, but it would surely be unwise to write him off; Djokovic is bidding to capture his fifth successive ATP World Finals title, and would move ahead of Pete Sampras and Ivan Lendl in the overall list of winners, equaling Federer with a sixth title. The Serb has never lost to any of his opponents in the Ivan Lendl group -- Gael Monfils (13-0), Dominic Thiem (3-0) and Milos Raonic (7-0) -- and still retains a 71% career win percentage against Murray.
• Titles in 2016: 7 - Roland Garros, Australian Open, Canada Masters, Miami Masters, Madrid Masters, Indian Wells, Qatar Open
• Aces in 2016: 264
• Win percentage in 2016: 88%
Milos Raonic, Canada, No. 4 – Already the first Canadian man to break into the ATP top 10, Raonic became the first to reach a major singles final when he met Murray at Wimbledon. That coveted first Grand Slam title may have evaded him, but he did take the Brisbane International at the turn of the year. Raonic nailed a slam dunk at the 2016 NBA All-Star Celebrity Game, helping Canada beat USA 74-64. And his 6-feet 4-inch stature also helps him on the tennis court ... He wins 90.6% of service games -- the third highest percentage on the tour in the past year (after Ivo Karlovic and John Isner) -- and has the fastest serve (career-best 155.3 miles per hour) of all the ATP World Tour finalists. The Canadian, 25, has also saved an impressive 70.2% of break points -- the highest proportion of the eight.
• Titles in 2016: 1 - Brisbane International
• Win percentage in 2016: 77%
• Aces in 2016: 824
Gael Monfils, France, No. 6 – For so long looked upon as an entertainer rather than a genuine threat, Monfils is making his ATP World Tour Finals debut in 2016, having produced a career-best season in his 30th year. He reached his first Grand Slam semifinal for eight years at Flushing Meadow, and though he may have eventually lost out to Djokovic, he boasts a higher break point conversion percentage than any other player at the finals. It's been a promising year for the Frenchman; consistency allied with his undeniable talent could see Monfils finally hit the heights he's hinted at.
• Titles in 2016: 1 - Washington Citi Open
• Aces in 2016: 471
• Win percentage in 2016: 75%
Dominic Thiem, Austria, No. 8 – The last man to qualify for this year's event, Thiem is the youngest player at the finals and the first Austrian to take part in the singles since former world No.1 Thomas Muster in 1997. He may have lost out to Djokovic at Roland Garros -- his first ever grand slam semifinal -- but boasts a 90.9% win percentage in deciding sets in 2016 -- the highest proportion of any player on the tour to have started 25 matches or more. Not bad at all for a 23-year-old.
• Aces in 2016: 462
• Win percentage in 2016: 72%
• Titles in 2016: 4 - Stuttgart's Mercedes Cup, Open de Nice Cote d'Azur, Acapulco's Abierto Mexicano Telcel, Argentina Open