Third seed Stan Wawrinka has had another successful season on the ATP World Tour in 2016, and the Swiss number one claimed his third Grand Slam singles title in three years at the US Open in September.
Kei Nishikori, the fifth seed has recorded consistent results in 2016 by reaching multiple Masters 1000 finals and another good run at the US Open by reaching the semifinals for the second time in three years.
Unfortunately for Nishikori, injuries have continued to intervene which has delayed his breakthrough on adding a big title to his cabinet on numerous occasions. At Wimbledon this year, he was forced to retire during his fourth round match against Marin Cilic.
Nishikori will be competing at the ATP World Tour Finals in London for the third consecutive year and he reached the semifinals on his debut appearance in 2014.
Magnus Norman has been an instrumental figure in Wawrinka's impressive form as of late. The Swede has been recognized for his hard work by being awarded the "ATP Coach of the Year".
Nishikori and Wawrinka are drawn in the John McEnroe Group which also features new world number one and three-time Grand Slam champion Andy Murray, and 2014 US Open champion Marin Cilic. This group has been dubbed as the "Group of Death", as it is significantly stronger than the other group.
Wawrinka's notable results leading up to London
Wawrinka was forced to miss the Rio Olympics on doctor's orders due to a back injury which could have been aggravated had he played in Rio. It proved to be a wise decision as the Swiss number one went on to win his third Grand Slam singles title at Flushing Meadows.
The third seed has a respectable 45-16 win-loss record in 2016 and has won four titles this year in Chennai, Dubai, Geneva and the US Open. However, since then, the results haven't been very good for Wawrinka's standards.
Following his triumph in New York, Wawrinka returned to competition at the St. Petersburg Open in Russia, reaching the 25th final of his career. The third seed boasted an 11-match winning streak in finals, however, he lost to Alexander Zverev in three sets, which was his first loss in a final since losing to Nicolas Mahut at the Rosmalen Grass Court Championships in June 2013.
At the Shanghai Rolex Masters, Wawrinka received a bye in the opening round and defeated Kyle Edmund in his first match but lost to Gilles Simon in the third round in straight sets.
More misery ensued for Wawrinka from the Zverev family as he lost to Alexander's older brother Mischa in the quarterfinals in his home event in Basel in three sets, and despite holding a match point at the BNP Paribas Masters in Paris, he lost to Jan-Lennard Struff in three sets.
Nishikori's notable results leading up to London
2014 US Open runner-up Kei Nishikori is the only participant in his group not to have lifted a Grand Slam singles or Masters 1000 title but the fifth seed has had the experience of reaching finals in both of those categories.
Nonetheless, Nishikori has performed well at Grand Slams and Masters 1000's in 2016 by reaching the quarterfinals at the Australian Open losing to an in-form Novak Djokovic, lost in the fourth round of the French Open and Wimbledon to Richard Gasquet and Marin Cilic respectively and lost to Wawrinka in the semifinals in New York.
Since his strong performance in Flushing Meadows, Nishikori's results have been mediocre. He took a few weeks off and returned to competitive tennis at his home event in Tokyo coming back from a set down to defeat Donald Young but injury struck and forced him to retire in the second round against Joao Sousa.
However, Nishikori reached his 20th final of his career and fifth final of the year in Basel defeating Dusan Lajovic, Paolo Lorenzi, Juan Martin del Potro for the first time all in straight sets and Gilles Muller in the semifinals in three sets but suffered his fourth consecutive final defeat in 2016 to Marin Cilic in straight sets.
At the final Masters 1000 event of the year at the BNP Paribas Masters, Nishikori was paired with Jo-Wilfried Tsonga in the third round, and the fifth seed held two match points on his own serve but failed to convert any of them, and subsequently lost to the Frenchman in three sets, who had an outside chance of qualifying for the ATP World Tour Finals in London.
Wawrinka and Nishikori have met on six occasions and the reigning US Open champion leads 4-2 in their head-to-head meetings and the third seed leads 1-0 on clay and 3-2 on hard courts.
Wawrinka won their first two meetings in 2012 both in straight sets in the quarterfinals at the clay court event in Buenos Aires, and in the fourth round of the Western and Southern Open in Cincinnati.
However, two years later in the quarterfinals of the US Open in 2014, Wawrinka and Nishikori both contested their best match to date against one another, and the three-time Grand Slam champion was the favorite coming into this contest as Nishikori had a long five-set battle with Milos Raonic in the previous round.
Nonetheless, Nishikori recovered from being a set down to dispatch that year's Australian Open champion, 3-6, 7-5, 7-6 (7), 6-7 (5), 6-4. The Japanese number one went on to reach his first Grand Slam final in the process.
Wawrinka didn't have to wait too long for his revenge by dispatching Nishikori in straight sets in the quarterfinals of the Australian Open in 2015, 6-3, 6-4, 7-6 (6).
Nishikori recorded his second victory over Wawrinka in the semifinals of the Rogers Cup in Toronto and it was a 7-5 (6), 6-1 victory, but it was revealed afterward that Wawrinka was suffering from a back injury.
Once again, Wawrinka didn't have to wait too long for revenge against the fifth seed as they met in the semifinals of the US Open a few months ago, and it was a 4-6, 7-5, 6-4, 6-2 victory for the eventual champion.
Wawrinka's victory in the process was Nishikori's first loss to a top ten player at the US Open.
Both Nishikori and Wawrinka come into this contest in mediocre form but both players know how to raise their levels when they are up against formidable opponents. Wawrinka's backhand has improved significantly over the years which has helped him secure three Grand Slam singles titles in his cabinet.
On the other hand, Nishikori's forehand is a deadly weapon when it is firing on all cylinders and he has got the best returners in the world, Novak Djokovic and Andy Murray firmly placed behind the baseline, unable to get a racquet on his shots.
The issue with Nishikori over the years has been injuries but when he is fit and injury-free, he is certainly one of the best top five players in the world, in terms of shotmaking.
Wawrinka will need to serve well against Nishikori as the fifth seed is a good returner, likewise, Nishikori will need to serve well and come to the net to shorten the points because the US Open champion has the firepower to dispatch Nishikori quickly.
Djokovic and Murray are the favorites to lift the year-end Championships in London and the duo are battling it out for the world number one ranking, however, Wawrinka will be flying under the radar and is more than capable of lifting this trophy.
This is the first match scheduled in the John McEnroe Group on Monday taking place on Centre Court at not before 2pm local time, and both players will want to get off to a strong start in this tough group.
Prediction: Wawrinka in three sets