When Novak Djokovic was awarded a huge silver trophy on Sunday to mark his achievement of finishing the year as world number - the fourth time in five years he managed the feat - it was difficult not to feel a huge sense of satisfaction for a man whose success means there is now a real possibility he could end his career considered the game's all-time greatest player.
Djokovic, who is chasing his fourth consecutive ATP World Tour Finals win at the O2 in London this week, collected his prize after demolishing eighth seed Kei Nishikori in his first group game of the season-ending showpiece event, winning 6-1 6-1 in just 65 minutes. It was his 15th consecutive win at the O2, a run that stretches back to 2011.
It was a superb start to the defence of his title, and the latest example of his growing superiority over the men's field. No one can touch the Serbian at present - even now, during the greatest era in men's tennis.
Nishikori is a talented player, but he had no answer to Djokovic's baseline brilliance. The world number one is relentless in his approach, grinding opponents down with a mix of stamina and unbreakable spirit. His court coverage is unrivalled, and for his opponents it can sometimes feel as though they are playing against a wall, such is the regularity with which the ball comes firing back towards them no matter what shot they produce.
It's been a special 2015 for Djokovic. He's won three of the four Grand Slams and was runner-up in one, with his defeat to Stan Wawrinka at the French Open in May the only blot on his copybook. He's supplemented his dominance in the Grand Slams with six Masters Series wins, a new record for a calendar year. He has 15,285 points in the ATP rankings - his nearest challenger, Andy Murray, has 8,470 - and his win-loss record for the year coming into this event was 78-5. A win here at the O2 would cap off his finest year as a professional tennis player.
Roger Federer remains the firm favourite with tennis fans across the world, and is rightly still regarded as the greatest male player of all time, but Djokovic looks likely to challenge his hegemony.
Federer is charming and stylish and possesses the most aesthetically pleasing game the world has ever seen. His service style, groundstrokes and movement across the court mean watching him is just about the most beautiful sight in sport. His 17 Grand Slam victories is an all-time record. He spent 302 consecutive weeks at number one, and between Wimbledon 2005 and the Australian Open in 2010 he made it to 18 of 19 Grand Slam finals. It's an impeccable record that has seen him elevated above previous greats Rod Laver, Bjorn Borg and Pete Sampras.
But things could be changing. Djokovic lacks Federer's charm and, indeed, his beauty on court, but his relentless baseline dominance, which sees him systematically dismantle opponents, means, right now, he is the best player on the circuit by quite some distance. He has 10 Grand Slams to his name and is just 28. He still has a few years at the top of men's tennis; years that he could dominate and close in on Federer's record.
It's becoming almost absurd how far and above the others he's become. Last week in the final of the Paris Masters against Murray, he was so dominant it became something of a non-event and left everyone wondering what on earth the British number one can do to make it to the top of the game. Murray himself has had en excellent 12 months, but Djokovic's record makes his look positively average.
Djokovic mercilessly punishes any mistake or any little dip in form. Tennis matches tend to ebb and flow. A player can firmly in the ascendancy one minute, only for momentum to shift rapidly the next. Very few players can produce their best throughout the entirety of a match, but for Djokovic, who is mentally incredibly strong, consistency is the norm.
He's won 23 consecutive matches and has collected 10 titles in 2015. He's out on his own at the top of the game, and by the time he has hung his racket up, he may well be in the conversation as to who the greatest ever player is.