Roger Federer says: “he is not feeling the pressure as he try to defend his ATP World Tour Finals crown and lift a record sixth season ending title.”
The 16 time Grand Slam champion has slipped to no.4 in the rankings but is confident of ending 2011 on a high.
"It would be amazing to win for the sixth time," he said.
Federer will finish the season without a major title for the first time since 2002 but he arrives on a 12 match unbeaten run and is confident of success.
"It's nice to be part of the top eight at the end of the season and have a chance to finish the year on an absolute high," stated the 30-year-old Swiss.
"There's always pressure as defending champion but I am used to it. I have done it so many times."
World number two Rafael Nadal said: "Being here is a big motivation. It’s one of the most beautiful courts in the world."
The world's top eight players will compete at London's O2 Arena for a third successive year, with Federer and Nadal both featuring in the opening round of matches.
On Monday, Britain's Andy Murray faces Spain's David Ferrer and, in the afternoon match, world number one Novak Djokovic goes up against Czech Tomas Berdych in the evening.