Even Roger Federer can suffer a crisis of confidence and the Swiss was quick to thank his new coach for restoring his after capping a vintage week at the ATP World Tour Finals on Sunday.

The 29-year-old Swiss played some of the best tennis of 2010 as he roared through to the final against world number one Rafael Nadal and he was at his flamboyant best again to beat the Spaniard 6-3, 3-6, 6-1.

Rewind back a few months, however, and there were those who thought Federer's aura had gone for good.

Defeat by Robin Soderling at the French Open ended his incredible sequence of 23 consecutive appearances in the semi-finals of grand slam tournaments and he suffered another quarter-final loss to Tomas Berdych at Wimbledon.

In between those two shocks he was beaten by Lleyton Hewitt on the grass courts of Halle -- his first loss there since 2002 and against a player who he had beaten 15 times in a row.

Drastic action was needed and Federer turned to American coach Paul Annacone, formerly with Pete Sampras, to compliment the work he was doing with fellow Swiss Severin Luthi.

It appears to have worked as Federer, who has often gone it alone without a full-time coach, has reached six finals and compiled a 35-4 record.

"First of all, I had to regain some confidence," Federer said after only his second win in two and half years over nine-times grand slam champion Nadal.

"That only comes through winning matches. After having somewhat of a disappointing clay season, Halle, Wimbledon stretch, where I wasn't able to win any tournaments and didn't play my best tennis, played a bit passive, it was important that I was able to pick up my game.

"I started moving better, started feeling well physically and mentally. I'm sure Paul has helped in this regard. So has Severin. He's helped as well over the last few years.

"That's why I'm very happy with my team at this stage of the season. I can obviously thank them for great work. It's through their hard work and my condition trainer, my physio, my wife and kids and everybody.

"It's been intense at times but it seems like we made many right decisions towards the end of the season. My body was able to cope with a lot of playing I did. I've played five tournaments in seven weeks but I feel very happy right now."

While Nadal has been the outstanding player this season, winning the French Open, Wimbledon and the US Open, Federer underlined just how important it was for him to win the year-ending title for a record-equalling fifth time.

In a tournament featuring the world's top eight players he won five matches, dropping just one set in the process.

"I'm really thrilled the way I played all week," he said. "To win a fifth time is obviously amazing, for the third time in a different place after Houston and Shanghai.

"I'm just really happy the way I was able to finish the season in style, really saving the best for last.

"Today was another great match with some fantastic rallies. I know it doesn't take anything away from Rafa's great season, because it was magnificent."