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Novak Djokovic insists he is willing to defy his flagging energy levels in a bid to finish the campaign with more glory at the ATP World Tour Finals.
The defending champion booked his spot in the semi-finals at London's O2 Arena by defeating Argentine fourth seed Juan Martin del Potro 6-3, 3-6, 6-3 on Thursday.
It was Djokovic's 19th straight victory dating back to his US Open final defeat by Rafael Nadal.
The Serbian only arrived in England on Sunday night after winning his third straight title at the Paris Masters and fatigue has inevitably been his biggest opponent to date at the season-ending showpiece.
But Djokovic is showing once again that his appetite for victories and titles has no limit.
"I had a great start of the season and now a great ending of the season," he said.
"I just feel good at this particular part of the year. I know most of the players are exhausted physically, mentally, emotionally, after a long season.
"But I try to find that as an opportunity for me to get extra motivated to push myself to the limit and deliver the goods when needed."
Djokovic discovered on Wednesday that his bid to finish the season as world number one had failed after Nadal wrapped up top spot in the year-ending rankings.
But the world number two showed no signs of letting that disappointment affect him as he continued his bid to retain Tour Finals title
"It's not frustrating for me. Actually I'm very encouraged by the way I've played over the last two months," Djokovic said.
"I'm playing the best tennis I think I played throughout the whole season. That's something that I take as a positive for this moment and for next season.
"I'm definitely feeling confident, more confident than I was a few months ago.
"Nadal has ended as number one in 2013 and he deserves that. No question about it.
"He won two Grand Slams. He played the best tennis this year."
This match was a meeting between the two form players of the autumn, with Del Potro having won two trophies and lost to Djokovic in the final in Shanghai over the past six weeks.
It was also a repeat of one of the best matches of the season when Djokovic won a five-set thriller in the Wimbledon semi-finals.
They delivered another hard-fought encounter and Djokovic admitted it was tough to subdue the big-hitting former US Open champion.
"I played a poor game at 3-2 in the second set and he used his chance to come back into the match," Djokovic said.
"Just a little bit of a lack of concentration on his side, on my side, decided this match.
"He has one of the biggest serves in the sport. He has one of the most aggressive forehands. I just needed to stay tough.
"I saved a few break points at the start of the third set. I had opportunities at 3-2 and I used them. He made unforced errors from the forehand side. I just tried to make him play. I served very well towards the end of the match."