London - Juan Martin del Potro believes he can muscle his way into the world's top four next year after returning to the kind of form that propelled him to the US Open title three years ago.
The 1.98 metres tall Argentine saw his bid to win the ATP World Tour Finals ended by world number one Novak Djokovic on Sunday but there was enough evidence in his three-set defeat to offer real hope that he can challenge for the big prizes.
Del Potro, who reached the semi-finals at the season-ender in London with a second win over Roger Federer in as many weeks, was irresistible for a set against Djokovic before fading to lose 4-6 6-3 6-2 at the O2 Arena.
Safely back inside the world's top 10 after a series of wrist problems, Del Potro is regarded as the man most likely to break up the status quo in the men's game and it was easy to see why on Sunday as he pummelled Djokovic early on.
His forehand wrought havoc in the opening set and his serve was brutal at times before he ran out of steam.
Despite defeat, Del Potro can look back on an injury-free year in which he reaped 65 match wins - 11 more than in 2009 when he stunned Federer to claim his first grand slam title.
"I think I'm playing good," the 24-year-old Tandil native, who beat Djokovic to win the Olympic bronze this year, told reporters. "I don't know if I'm playing better than 2009 but being in the semi-finals in this tournament was so big for me.
"These kind of matches give me illusions for the next season. I beat Roger on Saturday. I was close to beating Novak on Sunday. But in the end, they are too good for me.
"But I'm getting closer every day. It's my big challenge for next year, my big goal. Trying to fight at all the grand slams with this group. You know, they are winning all the grand slams: Novak, Federer, Rafa (Nadal) and now (Andy) Murray. I would like to be part of that in the grand slams."
Del Potro was a set and a break ahead against Djokovic before losing 11 of the last 14 games - a possible reaction to his three-set victory over Federer on Saturday.
"I think I played two good sets today," del Potro said. "But in the end, the difference is he's the number one in the world so if you don't play the whole match at your best level, it's really difficult to beat him."