Federer – who has 20 Grand Slams to his name – is the most decorated male player of all time.
The Swiss legend appeared on Bear Grylls’ TV programme on ITV on Monday night in which he undertook a survival course in the Swiss Alps.
Although he has had a number of his defining moments, the world No 3 has one that stands out.
And he has highlighted his epic five-setter victory over Nadal in the final in Melbourne last year as being very special.
“Somehow I was able to turn it around,” Federer said when asked how he clawed things back after trailing in the deciding set in the final.
“It was one of the most beautiful wins in my entire career.
“I waited until 35 to do it.
“I’m still on cloud nine!”
Federer lost his opening singles tie in the round robin stages of the ATP Finals on Sunday against Kei Nishikori.
And Sky Sports pundit Peter Fleming expects Federer to bounce back against Dominic Thiem.
“I think he will play better. The first match is always difficult in any event especially against a top player like Nishikori,” former American tennis player Fleming said.
“There’s no question Federer will play a lot better.
“He has to win.”
Should Federer triumph in London, it will be the 100th title of his career, leaving him nine short of Jimmy Connors’ record.