(CNN) -- The immediate future of the ATP Tour's showpiece event was confirmed on Wednesday, and that news was quickly followed by proof that men's tennis has another classic rivalry to savor.
Novak Djokovic and Andy Murray are longtime friends, but their on-court clashes are showing all the hallmarks of following Federer-Nadal, Borg-McEnroe, Sampras-Agassi and Edberg-Becker in the annals of modern greats.
Murray may have had the better of their meetings at the Olympics and the U.S. Open, but Djokovic hit back in Shanghai and now the Serbian has a 9-7 career advantage after another tight tussle in London.
The UK capital's hosting of the ATP World Tour Finals has been confirmed for the next three years, ending fears that it would move because of top players' unhappiness over the country's tax laws for top earners.
Djokovic won the season-ending tournament in 2008, its last year in Shanghai, but has not reached the final since.
Last year he didn't even make it out of the group stage, fading with fatigue after a breakthrough 12 months that he ended as world No. 1, but Wednesday's 4-6 6-3 7-5 win in more than two and half hours was his second in a row this week.
It was a match that see-sawed either way, leaving world No. 3 Murray needing to win his third and final match against Jo-Wilfried Tsonga on Friday if he is to progress in the elite eight-man event.
Tsonga also has a win and a loss after being beaten 7-5 3-6 6-1 by Tomas Berdych in Wednesday's late match.
"It was another great match, another great performance from both of us. I hope that people who watched it agree with my opinion," said Djokovic, who plays his final match against sixth-ranked Czech Berdych.
"I didn't expect anything less other than a tough match that went down the wire and was decided on the last point."
It was the sort of match that has helped bring in 250,000 people each year to London's O2 Arena.
"This week we look forward to welcoming our one millionth fan through the gates since 2009," ATP Tour chief executive Brad Drewett said after announcing the extension of the tournament's sponsorship deal with banking group Barclays.
"We thank every one of these passionate tennis fans for helping to create the electrifying atmosphere at The O2, which has offered a spectacular stage for our biggest event."
While the tournament, which attracted a television audience of 70 million viewers in 184 countries last year, does not have the prestige of the sport's four grand slams, the stakes are high -- the prize purse increased to $5.5 million this year and will climb to $6.5 million by 2014.
Murray cut a forlorn figure last year when he pulled out after his opening match due to injury, but this season he has won his first grand slam under the tutelage of Ivan Lendl -- a five-time winner of the ATP showpiece.
"In about the last two minutes of the match probably is what decided it," the Scot said of his latest clash with Djokovic.
"He broke from 15-40 and then I had 15-40 in the next game and didn't break.
"I think both of us probably see each other's games pretty well. Especially this year, because we've played so much. You kind of know a little bit what to expect.
"I think that's why all the matches, especially the last few, have been so close and decided by a few points. The intensity of my matches with him have been extremely high this year.
"I think both of us probably have seen things in each other's games improve and that's why there's a lot of long rallies and the matches are incredibly tight."
They both have some way to go before matching Roger Federer, who has won the tournament a record six times and on Wednesday was named the ATP Tour's most popular player by fans for the 10th year in a row.
The 31-year-old, who conceded the year-end No.1 ranking to Djokovic when he decided against defending his Paris title last week, also won the ATP's top sportsmanship award -- voted for by his peers -- for the eighth time in his career.
"We have great matches all over the world, and the recognition is a great feeling. We're trying to inspire the next generation," said the 17-time grand slam champion, who beat Janko Tipsarevic in his opening round-robin match on Tuesday.