Melbourne - Will Djokovic, Nadal and Federer dominate the Australian Open again, or is it time for a new young prince to become king?
ALSO SEE: 5 women to watch at the Australian Open
AFP Sport selects five men to watch when the season's first Grand Slam begins in Melbourne on Monday:
Losing the ATP Final to Alexander Zverev could not take the gloss off a 2018 season that ended with what Djokovic, now 31, dubbed "five perfect months".
The Serb made an astonishing climb back from outside the world's top 20 in June, winning Wimbledon and the US Open on the way to reclaiming the number one ranking in November.
It was all so different a year ago in Melbourne where a sorry last-16 exit at the hands of South Korea's Chung Hyeon was followed by elbow surgery and a string of early tournament exits. Now he returns at his supreme athletic best looking for yet another triumph at his favourite Rod Laver Arena where he has won six of his 14 Grand Slams.
The world No 2 also endured a disappointing Australian Open exit last year, forced to retire in pain from his quarter-final with Marin Cilic.
He missed most of the next three months and has to carefully manage the workload on his creaking 32-year-old body, battered by years of his all-action style. The 17-time Grand Slam winner sensibly cut short his 2018 season after bookending it with another injury retirement in the US Open semi-final.
Despite his truncated campaign he still managed to win five tournaments including a record-extending 11th French Open. Worryingly, he pulled out of the Brisbane International last week with a thigh strain but then played an exhibition in Sydney and insists he will be ready for Melbourne.
Two years ago the Swiss master came to Melbourne being written off as yesterday's hero only to confound the doubters and his advancing years by lifting a first Grand Slam crown since 2012.
Federer hasn't lost a match at the Aussie Open since his 2016 semi-final defeat to Djokovic and is going for a third successive title and record seventh in all.
He also bagged the 2017 Wimbledon crown in between for good measure, and the 37-year-old world No 3 will take his all-time record Grand Slam tally to 21 if he can summon up the spirit that propelled him to an epic, emotional five-set final win over Marin Cilic last year.
The world No 4 has widely been touted as the next king of tennis after a breakthrough 2018 season culminated in the 21-year-old German beating Federer and Djokovic in successive days to win the ATP Finals in London in November.
But for a player ranked in the top five since September 2017, he punches desperately below his weight in Grand Slams. He has only one quarter-final appearance, losing to Dominic Thiem at the 2018 French Open, to show from his 14 majors to date.
He has never made it beyond the last 32 in Melbourne and knows that must change this year if he is confirm his status as the flag-bearer for a new generation.
Australians would love to see a home winner and Kyrgios may be their best hope but, like most tennis fans, they never know quite what to make of his maverick talent.
At his sublime best the world No 51 has an unreturnable serve and the talent to topple anyone, but the temperamental 23-year-old has been talking to psychologists and "trying to get on top" of his mental health after another roller-coaster 2018 season where he was criticised for his on-court antics.
"I probably left it a little too long," he admitted after becoming notorious for his on-court meltdowns - he even needed a controversial umpire pep-talk to get him going during a US Open match.
Love him or hate him - but don't take your eyes off him.