It was framed as a question but it sounded more like a threat. Novak Djokovic was merrily destroying the hopelessly outmatched Kei Nishikori on Saturday night when a cry from the stands at the O2 Arena threw the narrative forward to the following evening: "Are you watching, Andy Murray?"

The crowd chuckled nervously and it was difficult to find too many optimistic Murray fans before he faced Djokovic in the final match of the year. Murray had taken so long to win his epic match against Milos Raonic at the ATP World Tour Finals on Saturday afternoon that he was walking into his press conference around the same time that Djokovic began a clinical humiliation of Nishikori. That seemed to confirm the Serb was finally back to his fearsome best after a wretched few months that began with his shock defeat to Sam Querrey in the third round of Wimbledon and resulted in him dropping to No2 in the rankings after Paris two weeks ago.

With Roger Federer and Rafa Nadal injured, Murray was the man to capitalise on his oldest rival's sudden slump, which featured fitness concerns, whispers of problems away from the court and defeats to players he normally eats for breakfast. The Scot secured his status as one of Britain's greatest athletes by winning his second Wimbledon, defending his Olympic title and rising to world No1 for the first time in a career that has been defined by his staggering ability to fight until the very last ball.

Surely, though, holding off a rejuvenated Djokovic in the battle to finish the year as the world No1 would be beyond even his powers of resilience. Typically Murray had reached the final after choosing the long route, beating Raonic in a record three hours and 38 minutes, while Djokovic had cruised through an easy group before dismissing Nishikori in 66 minutes. Murray was weary. Djokovic was fresh. There could be only one outcome.

It was a routine victory in the end, just not the one that most people had anticipated. Fighting off the fatigue, willing himself over the line, Murray once again demonstrated why no one can dispute his new status as the world’s dominant player, capping off the year of his life by outplaying, outwitting and outlasting Djokovic in an hour and 42 minutes of superb tennis.

Murray's 6-3, 6-4 win ensured he finished the year at the top of the rankings, a wonderful achievement by a man whose willingness to scrap and hustle and run as if his life depended on it sets the example for every rising star in his sport. The thought occurs that Murray's young friend, Nick Kyrgios, who was recently banned by the ATP after one misdemeanour too many, should be watching and learning.

Murray has had to drag himself off the canvas more times than he probably cares to remember. The early years were defined by agonising defeats in big matches, usually at the hands of Djokovic, Federer or Nadal. Even after winning Wimbledon for the first time early retirement was a distinct possibility before he underwent back surgery three years ago. He struggled after that operation and he had to be patient as he watched Djokovic pull away from him.

The stats pointed to a Djokovic victory before their 35th meeting. He had never lost an indoor match to Murray, had won 14 of their previous 15 encounters on hard courts and often looks as though he knows precisely how to get inside the Scot’s head and unsettle him.

It nearly happened at the end of the second set. Trailing by a set and two breaks Djokovic converted his only break point to spread anxiety around the arena, heightening the tension to the point where the umpire was forced to ask the crowd to respect both players. He briefly appeared to have located the warrior spirit that has helped him win 12 majors when he raised his level to save two championship points.

When Murray earned a third opportunity he netted a first serve. On another day Djokovic might have pulverised his second serve. But he had already butchered two simple smashes. His backhand rarely convinced, he often looked unsteady and his final forehand drifted long. Murray stuck to his plan, took his chances and stayed cool in the key moments.

Hiding his exhaustion well, Murray’s performance showed how much he has progressed in these past six months. He has crumbled against Djokovic in the past. No one saw them as equals when Djokovic crushed Murray in the Australian and French Open finals earlier this year. But it takes guts to keep coming back for more. Murray has been rewarded for his persistence. This was his 25th consecutive victory and it was the sweetest of the lot.

(Guardian service)