Just 12 months ago, Nadal was sitting at home in Manacor watching the ATP World Tour Finals on television as he contemplated the depressing thought that he may never again get the chance to compete for the sport's top prizes.

At the time the Spaniard was in the midst of a draining battle to recover from a severe bout of the knee tendinitis which has plagued him for years and, with no cure in sight, he was starting to fear the worst.

But fast forward one year and Nadal's present and future suddenly look a whole lot brighter.

The 27-year-old eventually found a solution to ease his knee pain and, after returning to the Tour in February, he quickly made up for lost time.

Nadal, who was fifth in the world when his comeback started, won the French and US Open titles, as well as eight tournaments, and in the process reclaimed top spot from Novak Djokovic — a supremely dominant run which reached a new peak at the Tour Finals in London on Wednesday.

He arrived in England knowing two wins in Group A of the round-robin event would ensure he finished 2013 top of the world and he did just that, defeating Swiss seventh seed Stanislas Wawrinka 7-6 (7/5), 7-6 (8/6) after beating David Ferrer 24 hours earlier.

Nadal's majestic career has featured many highs, among them eight French Open crowns and two Wimbledon titles, including a breathtaking five-set win over Roger Federer in the 2008 final, but even he felt little could surpass this glorious comeback.

"During all this season I said finishing top of the rankings was not my goal, but the truth is after all the success I had during the season, I think that after all what happened last year, I felt I deserved to be there at the end of the season. And today I did it," Nadal said.

"It was one of the best things that I did in my career, to come back to the number one after three seasons.

"That's very difficult in our sport, and after a very important injury. That's an emotional thing for me."

Initially, Nadal was more focused on proving he could still compete at the very highest level when he returned to action, but he said the number one ranking became important to him after he beat Djokovic in the US Open final.

"I think it's a great effort because I have unbelievable competitors in front. That makes the year end number one very, very special," he said.

"You can feel how tough everything is that winning all the things that I won this year, until the last tournament, I was not able to secure it. So that makes everybody realise how difficult it is to be there."

Now Nadal can cap an incredible campaign by winning the prestigious season-ending Tour Finals for the first time, with his victory over Wawrinka securing a place in the semi-finals with one group match still to come.

"To qualify for the semi-finals as well makes it an extra special thing," he added.

"And the good thing is after two matches now I can really be focused only on the tournament because the year-end ranking is over."

The only dissenting voice in the rush to praise Nadal came from Wawrinka, who was unhappy that the Spaniard received loud and regular advice from his coach and uncle Toni, who was sitting court-side.

"It's nothing personal against Rafa or against Toni. We all know, players and umpires, that Toni is always trying to help Rafa. That's normal. But when it's too much, it's too much," Wawrinka said.

"Today I didn't agree with the umpire not giving him a second warning. We all see. Before every point, he (Toni) was trying to coach him."