The 2018 season is already upon us, and if 2017 was anything to go by, it should bring numerous surprises. Here’s how several players stand going into the New Year.
Rafael Nadal and Roger Federer
Nadal and Federer dominated last season, with each winning two Grand Slam titles and finishing the year ranked No.1 and No.2 in the world.
Historically, seasons of that magnitude prove tough to replicate and Nadal, who ended the 2017 season with some pain in his knee, goes into 2018 with some questions marks over his fitness.
Even Federer, who has embarked on his 21st professional season in rude health, has warned that "it's not normal and realistic to aim for the same things I did this year in 2017."
Nevertheless, 2017 proved once and for all that neither player can be counted out until the day they retire, and the Australian Open and Roland Garros will likely start with Federer and Nadal as the respective favourites, barring any further injury issues.
Of course the Australian Open, where they played in the final last year, could change their equations depending on how well they perform.
The clay court patch will also have a huge say on how the pair's seasons pan out. Federer could pick up new ranking points - and potentially the world No.1 berth - if he plays tournaments on the red dirt, but those pose risks for his back and overall health, a chance he may not be willing to take with another Wimbledon title potentially in the offing.
As for Nadal, that part of the season remains essential, and will likely form the focus of his year. If he does well there, his confidence rises. If not, his ranking could fall by a lot.
Last year she won the Australian Open while pregnant and then didn’t play another match all year. At 36 years old, she should be near the end of her career - except Williams somehow looks younger and stronger than anyone would expect.
Whenever she enters a tournament, she’ll be a potential champion, and even motherhood is unlikely to stop her.
While winning a Grand Slam as a mother would rank among her most inspiring acheivements in tennis, it's one that could easily come to pass.
Against many expectations, Williams returned to court at the start of 2018 against Jelena Ostapenko, and took a set off the French Open singles champion in an exhibition defeat that held promise for the season to come.
New threats have emerged in her absence - including Ostapenko herself - but Williams remains just one Grand Slam title short of Margaret Court's all-time record of 24. She definitely wants to tie and beat that mark, and she has plenty of energy to try.
The Australian Open may come too soon for her to reach her formidable best, but 2018 could well yield at least one more Grand Slam title, particularly at Wimbledon, where she is unbeaten in singles since 2014.
Will the once top-ranked male players make comebacks this year? Novak Djokovic, Andy Murray and Stan Wawrinka are about to find out.
All have been absent for long stretches, and all three have been forced to withdraw from season-opening tournaments due to lingering injury problems. Confidence and ring-rust will likely be issues for the trio upon their returns, but their desire to simply get back to doing what they do best, let alone win titles, should not be underestimated.
Should any of the three rediscover their form and fitness, then they will have a significant say on the destination of the year's biggest prizes.
Djokovic is perhaps the most intriguing of them all. Where the all-time Grand Slam singles title record once appeared in his sights, last year saw it move further out of reach, with the Serbian failing to win a Grand Slam singles title for the first time since 2010.
Now he has a new coach, Radek Stepanek, a potentially inspired choice that could restore the Djokovic's famed determination and fight. Soon we’ll see how much ambition and confidence the 12-time Grand Slam singles champion has been able to regain in training.
Garbiñe Muguruza and the rest
Ranked No.2 in the world and now a Wimbledon singles champion, Muguruza could be the first of the young players to take over women’s tennis.
How likely is this? The WTA side of the Grand Slams remain wonderfully unpredictable, and with Serena Williams back in the picture, there could be old-school dominance once again.
But Muguruza seems to be adding staying power to her list of attributes, and best of all, she is still improving. Her performance in Australia could get her off to a fast start.
Elsewhere, former world No.1 Angelique Kerber will hope to banish memories of a disappointing 2016 that saw her drop out of the world's top 20, and where better to do that than Melbourne, the site of her first Grand Slam title?
Simona Halep made huge strides last year, but will no doubt be striving for that statement Grand Slam victory to go with her world No.1 ranking, having been denied in the Roland Garros final.
And then there is Maria Sharapova, who, in her first year since being suspended, played well at the US Open, beating Simona Halep in the first round before running out of steam. Her season was acceptable, but Sharapova clearly expects more and has a lot to do to get there.
At age 30, she’s still young enough, by today’s standards, to compete for Grand Slam titles. The question is whether she can stay away from injuries for a long stretch so she can return to the form she once had.
The new champion?
Alexander Zverev is 20 years old and arguably the most talented young men’s player in the game. His groundstrokes are electric and his serve powerful and consistent, with both helping him to a career best five titles in 2017, two of which were Masters.
Yet in the game’s biggest events - the four Grand Slams - Zverev has suffered several disappointments. This season, at last, could be his breakout year, depending on his belief and his ambition. Look for Zverev, now ranked No.4, to push hard for a title at the Australian Open.
The 'lost' generation
In between the young guns and old guard of the men's game lies the so-called 'lost' generation, a collection of 20-something players that have promised much but been unable to claim the game's grandest prizes.
But is an awakening in the offing? Certainly last year's ATP Finals seemed to suggest so, with Grigor Dimitrov and David Goffin contesting a high-quality final in London. At world No.3 and No.7 respectively, and with some of the game's biggest names struggling for fitness, both men look well positioned to fight for Grand Slam titles.