Novak Djokovic
Novak Djokovic completed his dominant year by lifting the ATP World Tour Finals trophy. Getty Images

The 2015 tennis season officially came to a close on Sunday, with Great Britain’s win over Belgium in the Davis Cup final. And yet there is little time for the top players to recover and regroup, with the 2016 campaign getting underway on Jan. 4, and the first Grand Slam of the year, the Australian Open, beginning just two weeks later. That provides just about enough time to reflect on the season that was; one in which the Big Four showed that they are likely to remain a force to be reckoned with over the next 12 months.

Novak Djokovic (Year-end ranking No. 1)
The Serbian absolutely dominated 2015, finishing with not far off double the points of his nearest challenger. Only a shock defeat to Stan Wawrinka in the final of the French Open prevented Djokovic from winning a Calendar Slam, having picked up the titles at the Australian Open, Wimbledon and the U.S. Open. Close to unbreakable, either physically or mentally, Djokovic completed one of the finest years in tennis history, winning six Masters 1000 titles, the ATP World Tour Finals and 11 titles overall, losing just six of his 88 matches. At the age of 28, he is now in double figures for Grand Slam titles and it is very difficult to imagine him not adding to that haul in 2016.

Andy Murray (Year-end ranking No. 2)
No player was on the receiving end of Djokovic’s exceptionalism in 2015 more than Murray. The Scot suffered six defeats to his long-time rival, including in the Australian Open final, which was as close as Murray came to adding to his two Grand Slams. Yet despite those facts, it would be hard to say that Murray’s 2015 has been anything other than a major success. It shouldn’t be forgotten that he came into the year after a troubled 2014, in which he only showed signs of his best in the final weeks.

And yet the year ended with him finishing ranked at No. 2 for the first time. Along the way, he also claimed his first two titles on clay. Yet 2015 will undoubtedly be remembered as the year in which Murray led Great Britain to the Davis Cup for the first time since 1936. The 28-year-old won all 11 of his matches in singles and doubles, and it was clear that as Britain progressed, the tournament became Murray’s priority. Fresh from the emotional boost, Murray will now look to seriously challenge Djokovic in 2016.

Roger Federer (Year-end ranking No. 3)
The very fact that Federer continues to sit near the top of the rankings and be a serious contender to land Grand Slam titles at the age of 34 is a remarkable achievement. Picking up six titles, equaling his biggest haul since 2007, it has been another memorable year. Incredibly, given all that the 17-time Grand Slam winner has achieved, he has also found ways to innovate and even improve. Over the past 12 months he has produced some of the best serving performances of his career, finishing third on the ATP Tour for percentage of first-serve points won, while adapting a thrillingly aggressive strategy.

The only disappointment was that he failed to add to his record haul of Grand Slam titles. For that he has Djokovic to thank. The Serbian beat Federer in the final of both Wimbledon and the U.S. Open. And, while it would be easy to suggest that his best chance of winning Grand Slam 18 has passed, it would be foolhardy to write the Swiss great off.

Rafael Nadal (Year-end ranking No. 5)
This year has undoubtedly been the most challenging of Nadal’s career. In 2015, the Spaniard dropped to his lowest ranking, No. 10, in a decade, and for the first time since 2004 he failed to win a single Grand Slam title. Indeed, Nadal didn’t even make it into the semifinal of any of the Grand Slams, with the nadir arriving when blowing a two-set lead to Fabio Fognini in the U.S. Open third round. The most painful moment, though, was surely the ending of his dominance at Roland Garros, when Djokovic breezed past the nine-time champion in the quarterfinals.

And yet there is reason for hope going into 2016. Nadal began to show more consistent examples of his relentless best in the final weeks of the season, and enjoyed a straight-sets demolition of Murray in the ATP World Tour Finals en route to the semifinals. While how long his body can hold up will always be a major question mark, the 29-year-old appears to be getting his confidence back in time to become a real threat again in the year ahead.