Andy Murray heads into the Barclays ATP World Tour Finals insisting 2009 has been the best year of his career - but admitting the pressure is growing to break his grand slam duck.

The British number one has won six tournaments this year - more than anyone else on the ATP Tour - but his failure to triumph at one of the four majors continues to hang over him.

Expectations were sky high after his US Open final appearance last year but a semi-final defeat by Andy Roddick at Wimbledon was the best he could manage this season.

And Murray, who will take on Juan Martin del Potro in Sunday's opener at the O2 Arena in London, knows victory in the prestigious season-ending tournament would be a big step towards winning on the biggest stage of all.

The 22-year-old said: "This tournament is just behind the grand slams, because you have to win five matches or four matches against the top players in the world.

"You might even have to beat the number one or number two in the world twice to win the event so it's not quite the same as a grand slam but it's a huge, huge tournament.

"Everyone views it a little bit differently but I still believe that I have a few chances, maybe one or two more chances, to win a grand slam.

"For me, the year's been a successful one. For some people grand slams are the be-all and end-all. I want to win one, I'm trying my best to win one and I'll work as hard as I can.

"I feel like I'm getting closer than I was a couple of years ago. I feel I'm a better player than last year. I had a few problems at the grand slams this year. The ones I didn't do so well in, hopefully next year I'll feel great going into all of them.

"My consistency this year has been superb. Physically I've felt like I've been a lot better this year.

"I've not had any real let-downs in any tournaments except in Rome - I've lost one first round the whole year, which is better than previous years.

"I've got a better record against all the top players this year so it's been my best year on tour without question and hopefully next year will be better."

Murray has been drawn in the same group as US Open champion Del Potro, world number one Roger Federer and Fernando Verdasco for the round-robin event, with Rafael Nadal, defending champion Novak Djokovic, Nikolay Davydenko and Robin Soderling in Group B.

The Scot only returned to action this month after six weeks out with a wrist injury and, although the joint is no longer giving him problems, he admits he goes into the event unsure of his chances.

"I'm not putting too much pressure on myself this week," he continued.

"I'm not expecting to go out there and play great. I might go out and do well because of that.

"Obviously I haven't played too much in the last two or three months so I don't know exactly what to expect. Mentally I feel fresh and that's going to be important."

Nadal's season was interrupted by a two-month break with knee problems, which prevented him defending his Wimbledon title.

Question marks remain over his fitness and he goes into the end-of-season tournament looking for his first title since the spring.

The Spaniard, though, is buoyant about his form, saying: "I've had the best end of season in my career, it's been almost perfect.

"I'm very close to my best and it's been a lot better than I expected when I (returned to the Tour) in Montreal."

A jackpot of more than US dollars 1.6million is available to an unbeaten champion but, with Federer and Murray having had time away from the Tour recently, Nadal not at his strongest on indoor courts and Djokovic having played almost 100 matches this season, picking a winner looks a difficult task.

And Federer, for one, is expecting a close tournament.

"I think the groups are even," he said. "The top eight guys have been very consistent and this year it's a bit more open than in the past."