The long season will finally conclude next week with the top eight players in the world competing at the ATP World Tour Finals.
Here's look at how the four players in Group B might fare at the O2 Arena in London. (For a breakdown of Group A, click here.)
2. Andy Murray
2015 record: 68-12, 4 titles
Season highlights: Murray has re-established himself as a force in the game. He opened the season with an auspicious run in Australia, reaching a Grand Slam final for the first time since winning Wimbledon in 2013. Murray also reached the semifinals at Wimbledon, where he fell to Federer in straight sets. But it should be noted that Murray had the misfortune of playing Federer in what was one of the Swiss' finest-ever serving performances.
Murray broke through in the clay season as well, winning in Munich and Madrid. He also came closer than ever before -- within a set -- of making what would have been a first French Open final, when he extended Novak Djokovic to five sets. If that wasn't enough, Murray has led his Great Britain squad to the Davis Cup final, which will be played the weekend after the ATP World Tour Finals.
Season lowlights: Murray succumbed before the quarterfinals of a major for the first time since 2010 when he fell to South Africa's Kevin Anderson in the fourth round of the US Open.
What to expect in London: For a while, there was a degree of uncertainty over whether Murray would compete in London. Murray suggested playing the year-ender on hard courts would complicate his preparations for the Davis Cup final against Belgium, which will be played on a clay court in Ghent, Belgium. But Murray decided he will play in London, even if he will spend most of this warm-up week training on clay.
But it's not as if he is lacking recent matches on hard courts after finishing runner-up to Novak Djokovic at last week's Paris Masters. Even after that run in Paris, Murray ought to be fresher in London than he was at the tournament 12 months ago.
4. Stan Wawrinka
2015 record: 53-16, 4 titles
Season highlights: The adventure and the audacity of Wawrinka's tennis against Djokovic in the Roland Garros final can be edited down to a couple of seconds of videotape. How did Wawrinka respond when he found himself pushed wide of the tramlines on Court Philippe Chatrier? Why, he only fired a backhand around the net post. "Whoa," exclaimed John McEnroe on the telecast. "How did do that?"
Still, even when Wawrinka played the ball over the net, rather than around it, there was nothing conventional or mundane about his backhands.
Pretty as it was to watch, Wawrinka's shorts weren't. He defied the fashion police at Roland Garros for his choice of attire, donning what is widely believed to be some of the ugliest shorts ever worn by a tennis player. In a moment of irony, however, the plaid-laden knickers were put on display at the Roland Garros museum.
Nonetheless, Wawrinka won the title, his second career major.
Season lowlights: Two months before the French Open, Wawrinka won only three games against Grigor Dimitrov in an early-round loss at Monte Carlo. "I didn't know where I was, but I wasn't on the court for sure," the Swiss told the media at the time. On the eve of the French Open, Wawrinka was understandably aggrieved when the tournament website published an article about his private life, which was under heavy scrutiny at the time.
Wawrinka was the centerpiece of further controversy during a hard-court tournament in Montreal when his opponent, Australia's Nick Kyrgios, dished out a distasteful remark about Wawrinka's girlfriend.
What to expect in London: This is the third successive year that Wawrinka has qualified for the season-ending tournament, and both previous times, he reached the semifinals. In fact, last year, he even held match points against Federer.
Wawrinka has the game and the mind to win in the white heat of competition. Perhaps we should already be speaking of a Big Five in men's tennis. If Wawrinka were to win this title, he will have secured two of the five most important tournaments this season.
5. Rafael Nadal
2015 record: 58-19, 3 titles
Season highlights: Despite an all-around down year, there has been some silver lining. Nadal qualified for the World Tour Finals and is ranked in the top five. Nadal won Stuttgart, his first grass-court title since Wimbledon in 2010. Nadal also won clay-court tournaments in Buenos Aires and Hamburg.
More recently, he reached the finals in Beijing (lost to Djokovic) and Basel (lost to Roger Federer). OK, Nadal didn't win those tournaments, but those runs were encouraging heading into London.
Season lowlights: For the first time since 2004, Nadal failed to win a Grand Slam title. To boot, he didn't come up victorious in a Masters event, either. Nadal lost in the second round of Wimbledon, the fourth time he has fallen to a player ranked No. 100 or lower on the lawns of the All England Club. Nadal went out in the third round of the US Open.
Perhaps, though, the most disconcerting of all Nadal's defeats was his loss in the quarterfinals of Roland Garros against Djokovic. Amazingly, that was only the second time in his career Nadal succumbed on the Parisian clay. He admitted self-doubt and a tentative forehand played a role in his less-than-stellar play.
What to expect in London: Twice Nadal has made the final of this tournament, but he has never won it, making it the most significant prize to elude him. Perhaps this won't be the year that he wins, but his recent performances suggest he should play some decent tennis on the Greenwich Peninsula.
7. David Ferrer
2015 record: 55-13, 5 titles
Season highlights: No one has ever denied Ferrer's work ethic, and this year, the Spaniard has been rewarded for his efforts, winning five titles. Aside from 2012, when he snared seven titles, Ferrer has never gathered so many trophies in a single year.
Ferrer is widely known as a clay specialist, but four of his five titles in 2015 have come on hard courts. A couple of those wins have come in the past two months, in Kuala Lumpur and Vienna.
Season lowlights: An elbow injury prevented Ferrer from having any involvement at Wimbledon, and he was also absent from most of the summer's North American hard-court swing. His only appearance came at the US Open, where he made the third round.
What to expect in London: It's been eight years since Ferrer, then a year-end debutant, played in the final of this tournament. Still, it's not as if he hasn't made an impression; in 2011, the Spaniard reached the semifinals.
While Ferrer doesn't have the profile of some of the other players in the competition, he does have the ability and the determination to make himself a nuisance at The O2 -- and thus shape an unforeseen narrative.