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World number one Novak Djokovic dedicated his victory over Roger Federer at the ATP World Tour Finals to his ill father.
The Serb beat Federer 7-6 (8-6) 7-5 to win the season-ending title at London's O2 Arena.
He later described how he had been motivated by his father Srdjan, who is said to be suffering from an acute respiratory illness.
"This was a title for him," said the 25-year-old from Belgrade.
"He's much better now. At a certain stage it was very critical. We didn't know what tomorrow brings, but now he's much better and he's recovering.
"He's still in intensive care. I'm going to visit him and see how it goes and try to bring the trophy with me and at least make him smile."
Djokovic admitted that his achievement of retaining the year-end top ranking felt comparable to his amazing achievements of 2011, when he won three of the four Grand Slam titles and racked up a 43-match winning streak (including two matches in 2010).
It came to a fitting climax in London on Monday, when he saw off an at-times rampant Federer with a performance of incredible grit and determination.
"All in all, it was a fantastic year where I've had to face a lot of difficulties off the courts as well," he said.
"Especially coming into this tournament, having my father fighting his own fight for health gave me extra strength that I wanted to play for him in a way, that's one of the reasons I really gave it all every match, especially tonight."
He added: "I actually feel more satisfied right now than last year, even though I had an incredible 2011.
"I feel this year, considering the circumstances that I had to face on and off the court, the expectations, all these things, has been even more successful for me."
Djokovic fell behind in both sets against Federer but over the course of two hours and 14 minutes he fought his way past the 17-time Grand Slam champion.
"He's somebody that's aggressive, that likes to finish his points very quickly" said Djokovic.
"Especially when he's a break up, he's probably the best player I ever played against, he comes up always with his 'A' game when he's up. It's very difficult to handle that.
"But I managed to gets lot of his shots back into the court, being passive, a couple of metres behind the baseline, coming into an aggressive position.
"That was one of the goals tonight, to always try to get him into the long rallies where I think I had the better chance."
And asked about the stunning backhand winner he made on match point, he added: "It's the best way to finish the match, I guess, with a passing shot - one of my favourite shots."