THERE has been a persistent movement for a decade or more to attempt to quantify the genius of Roger Federer in numbers.

It is understandable that a sportsman should be defined by what he wins and how many times, but any attempt to capture Federer with statistics falls short of the full story and cannot give it a proper substance.

The numbers, of course, need to repeated like the six-times table. It is, frankly, incredible that the Swiss player has reached 100 ATP finals. It was almost predictable that last night he won a record-breaking sixth Barclays ATP World Tour Finals by defeating Jo-Wilfried Tsonga of France 6-3, 6-7 (6-8), 6-3 in two hours 18 minutes. It is proper to acknowledge that he is the oldest man, at 30, to win the tournament and that his title was the latest in a 17-match winning streak.

However, this is all essentially the stuff that fills record books. One has to watch Federer to capture him in all his glory. This greatness is not confined to technique or the flashing brilliance he wields as if his racket was a light sabre. It is truly wonderful to watch Federer in full flow but it is deeply instructive to watch him struggle. He has the talent but, crucially, he has the will.

It is what carried him last night to his 70th title on the ATP tour. This was not the imperious Federer who dismantled Rafael Nadal earlier in the tournament. This was not Federer the untouchable, but Federer the winner.

There were moments last night that displayed this extraordinary desire to win. At 6.13pm in a packed O2 Arena, Federer hunched down to receive the serve of Tsonga. The Swiss player was 4-3 ahead but had only won one point on the Frenchman’s serve.

He was being battered by the world No.6. The power of the 26-year-old was overwhelming Federer. He prepared to meet the storm of Tsonga again. The great man won four of the next five points, taking the break. The set was subsequently won after a simple Federer service game.

This ability to seize the moment is necessary for the performer at the highest level but it has to be backed by a resilience. Federer, frankly, made a mess of the second set yet had the intelligence and strength to consign it to history. He served for the match at 5-4, he held a 5-2 lead in the tiebreak and subsequently he had a match point. He squandered the lot. A booming Tsonga forehand to win the set could have been construed as a signal that the flow of the match had change. Of course, it had not. Federer regrouped, refocused and set about winning the match again.

He has now played Tsonga on three consecutive Sundays – in Paris and then in the first round robin match in the tour finals – and has learned that patience must be employed when the big-hitting Frenchman launches his massive frame at the ball. Federer knows that it is all about creating opportunities and taking just one of them when they come. His moment came at 4-5. There was one, two and then a third break point. Federer converted it. Tsonga visibly wilted and the service game for the Swiss player at 5-4 amounted to a premature lap of honour.

“I could not be more happy. I could not be more exhausted,” said Federer, who has regained the world No.3 slot, as he received his trophy. This tiredness may not just be the result of an arduous season, but may owe something to longevity. Amid the celebrations it was sobering to note that Federer won his first tour finals title against Andre Agassi in what seems a different generation.

“He’s maybe the best player ever,” said a defeated Tsonga whose improvement this year, including a victory over Federer at Wimbledon, was not enough to end his season with a career-best triumph. “I need to improve again,” he said. “I have to work hard to make my body quicker on court, to move better. Maybe if I move better next year, I will have better results.”

Federer was gracious about Tsonga but unusually revealing about himself. He talked about the doubts he had suffered earlier in the season when grand slams victories passed him by and he lost, despite having a match point, to Novak Djokovic at the US Open.

He decided then to take a break from the game to reassess his life, his game, his priorities. He felt he had lost too many close matches. “I had to question myself to see if I had done something wrong.”

He added: “Maybe the doubts were just a bit too strong during certain moments.”

Typically, predictably, he has come back stronger. “I managed to find a way through,” he said of the tough moments in last night’s match against Tsonga. “The most important reaction is the one I show after losses.”

He now looks forward to 2012, not so much another year but another number in the Federer story.