Juan Martin Del Potro is confident he can challenge for Grand Slam titles next season after pushing Novak Djokovic all the way in the semi-finals of the ATP Tour Finals.
Del Potro was on the verge of a shock win over Djokovic when he led by a set and a break, but the world number one hit back in impressive fashion to win 4-6 6-3 6-2 at the O2 Arena.
The Argentine was disappointed to bow out but he takes plenty of positives away from London.
"Nothing happened to me - Novak just improved his game between the middle of the second set until the end of the match. He deserved to win today," Del Potro said.
"I played really well in the first two sets, but in the end he made the difference. 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."
His victory over Roger Federer on Saturday - ending the Swiss superstar's 12-match unbeaten run in the finals - was his highlight, and his performance against Djokovic, plus recent title victories in Vienna and Basle make del Potro believe he can once again win a Slam.
He won the US Open in 2009 but injuries to his wrist have prevented him making a sustained challenge to the top four.
"These kind of matches give me dreams for the next season," Del Potro said. "I beat Roger, I was close to beat Novak today. I'm getting closer every day.
"They have been winning all the Grand Slams; Novak, Federer, Rafa Nadal and now Andy Murray.
"Maybe it could be my big challenge for next year, my big goal, trying to fight for all the Grand Slams with this group."
"I think I'm playing well. I don't know if I'm better or not than 2009, but being the semi-finals in this tournament is so big for me.
"It was Federer, Djokovic, Murray and me. These big names are there in every big tournament. It's going to be my big challenge next year to be part of that group."