When Novak Djokovic won the French Open in early June, his lead at the top of the world rankings was more than 8,000 points. He had just beaten Andy Murray in a Grand Slam final for the third time in 18 months; their rivalry felt jaded because of its one-sided nature.
The announcement, just seven days later, of Ivan Lendl's return to Murray's coaching team caused a surge of optimism. But even after a second Wimbledon title was secured in July, and a second Olympic gold medal won in Rio in August, topping the world rankings before the year was out seemed inconceivable.
Murray's season has sometimes tailed off in the last few weeks of the year. Not in 2016. He has won 18 matches in a row to become the first British singles player to top the world rankings. Seventeen of those wins have come in the space of just 31 days, and he has now reached the final in 11 of his past 12 tournaments.
By reaching number one, Murray joins a select band of professionals. Only 25 other men have risen to the top of the rankings since the system was computerised in 1973, which is one of the reasons the position is so revered within the sport.
Roger Federer, Pete Sampras, Lendl, Jimmy Connors and Djokovic have all spent more than 200 weeks at the top, but greats such as Mats Wilander and Boris Becker will tell you just how hard it is to stay there. They won 13 Grand Slam titles between them, yet their spells at number one were relatively brief: 20 weeks and 12 weeks respectively.
Pat Rafter is another example. The two-time US Open champion became world number one on 26 July 1999, but by the time he played in Montreal a week later, he had been overtaken by Sampras and never regained pole position.
This has been a year in which Federer and Rafael Nadal have been taken out of the equation by injuries. Djokovic, too, has had physical (and personal) issues to contend with since the summer, but has still had a formidable year - winning another two Grand Slam titles, four more Masters Series events and finishing as runner-up at the US Open.
To overhaul him, Murray has already had to claim seven titles - won in five countries and three continents. He has competed in 10 countries this year, spending time in Europe, Asia, North America, South America and Australia. Had ranking points been on offer at the Olympics, his lead would be a handsome one.
Murray has won clay court, grass court and hard court titles. He has won indoors and outdoors. And, even if surfaces have become more homogeneous in recent years, this is another reason why the number one ranking is so treasured. Players are frequently asked to switch surface, climate and time zone to identify the very best in the world over a 12-month period.
|Total number of weeks ranked number 1|
This may be Murray's greatest achievement - he is the second oldest man in history to make his debut at number one - although I always find the magnitude of his first Wimbledon title hard to quantify, given the huge weight of history against him when he set out on his career.
It is not one of which he dreamt. The Murray brothers were more impressed by footballers and wrestlers in their formative years, with Andy sometimes assuming the persona of 'The Rock' and Jamie of 'Stone Cold Steve Austin' as they recreated wrestling bouts on the duvet, with pillows for weapons.
Murray's next task is to stay clear of the rest. And, first and foremost, to become only the 17th man in history to claim the year-end number one ranking.
If he does, he has an excellent chance to consolidate his position at the top, as after the Australian Open he has very few ranking points to defend until May.
But, whatever the future holds, Murray - like his brother - will forever be spoken of as a world number one.
He has spent much of his career emulating the achievements of Fred Perry, who is judged to have been the best player in the world for many years in the 1930s. For Murray, it's now official.