Juan Martin del Potro feels he still has a lot of work to do if he is to break into the world's top four.

The 21-year-old can reflect on a year in which he has really come of age, beating Roger Federer to win the US Open in September and then reaching the final of the Barclays ATP World Tour Finals at London's O2 yesterday.

A win would have taken him above Andy Murray into fourth in the rankings but he was beaten 6-3 6-4 by an inspired Nikolay Davydenko and will start next season 425 points behind the Scot.

Murray would have been entitled to feel somewhat aggrieved at dropping a place, given Del Potro pipped him for a last-four spot in London by only one game, but the Argentinian could potentially start the Australian Open in January in fourth because the British number one is not planning to play any ranking events beforehand.

Del Potro, though, is in no hurry. "I have to keep working," he said. "I have many things to improve: my serve, my forehand. My goal is to feel better with this part of my game so I can be in a better position.

"But I have very good players fighting with me, like Murray, (Novak) Djokovic, Federer, (Rafael) Nadal. So I know the way I need to work."

Del Potro claimed a second high-profile win over Federer to reach the last four at the O2 before edging Robin Soderling in a high-quality semi-final.

And although he came up just short in the end, he still reflected on a successful end to the season as the bigger names fell by the wayside.

"If I'm in the final, I want to win," he continued. "But here, all the players are very good. Maybe names like Federer, Djokovic, Nadal or Murray, everybody thinks they will be in the final. But it didn't happen. So I had a good tournament anyway."

Davydenko, meanwhile, can head to Russia celebrating the biggest win of his career - and the biggest pay cheque, with the 28-year-old collecting more than US dollars 1.5million for his week's work.

And, after flying under the radar for much of his career, Davydenko is now hoping he will start to enjoy a higher profile in his homeland.

"I hope, after this tournament, I will become more famous in Russia," he said. "For me, it's really important. It has always been disappointing, like in Moscow (in October) when I played against Marat (Safin).

"About 80% of the crowd were supporting Safin. For sure this was the last tournament (in Russia) for him. But I saw how many people like him, how they support him, how they enjoy how Marat played.

"I hope now Marat is retired, and in the future, I'll be famous in Russia and everybody will support me."

It was the sixth year in a row Davydenko had qualified in the top eight for the end-of-season event, the Russian also reaching the final last year before losing to Novak Djokovic.

But he played down his chances of returning to London to defend his title, saying: "Six years in a row coming in the top eight? I don't know if I can do it. It's going to be really interesting next year for me because winning the last tournament this year is something amazing."

Meanwhile, the 28-year-old had nothing but praise for the tournament in its first of five years at the O2.

"It is a good stadium and everything was perfect," he added. "We have Queen's Club to practise also. For sure we'll enjoy being here in London next year. I hope the organisation will be the same or better."