Andy Murray feels he must hit top form immediately to stand any chance of winning the ATP World Tour Finals.
Unlike all other tournaments on the tennis calendar, the year-end championship features only the world's top eight players.
"You have to be right on your game from the first match," said the Scot, who starts against David Ferrer on Monday.
"Sometimes you work your way into an event. Here you have to play your best, simple as that."
World number one Novak Djokovic added: "Everybody wants to finish off the season in great style and that's what makes this even more competitive."
London's O2 Arena plays host to the week-long competition for a third successive year.
Two groups of four players will face off in round-robin format, before the top two from each group advance to the semi-finals and vie for a place in the 27 November final.
It starts on Sunday when Roger Federer plays Jo-Wilfried Tsonga at 1400 GMT and Rafael Nadal takes on Mardy Fish not before 2000 GMT.
On Monday, British number one Murray meets Ferrer at 1400 GMT and Djokovic goes up against Tomas Berdych not before 2000 GMT.
"It's one of the biggest tournaments on the tour - you're competing against the top guys," Murray said. "If you can win, it's a big achievement, one of the biggest. So there's a real incentive.
"This is different from other tournaments because you have to play well - very good tennis - from the first match if you're to have a chance of going through."
Murray suffered a last-four defeat by Nadal in 2010 but this season has been the best of his career, reaching the semi-finals or better at all four Grand Slams for the first time.
While the wait for a first major title goes on, he arrives with 27 victories in his past 29 matches and a strong record on the O2 surface.
"I am most comfortable playing indoors because that is what I grew up playing on," said the 24-year-old Scot.
"Last year I lost in the semis but played a great match against Rafa. In some ways maybe losing that match gave me the drive to work harder and make sure things improved.
"As long as I finish the year playing good tennis, that makes a difference going into the off-season."
Murray holds a 5-3 head-to-head advantage over Ferrer but trails Berdych 3-1, including a recent loss at the Paris Masters, while Djokovic leads him 6-4.
"None of the matches are easy and there's no group you're going to get that's going to be much better than the other one," Murray said.
"I've played well against Ferrer on hard courts in the past but he's made the final before [in 2007] and he has won tournaments on indoor hard courts.
"Berdych played very, very well in Paris and obviously Novak, even though he's had some injury problems the last few weeks, has had an incredible year.
"It's going to be a tough draw, with long points and long matches."
Djokovic has enjoyed a phenomenal year, winning the Australian Open, Wimbledon and US Open and taking over from Nadal as the new world number one.
Abdominal and shoulder injuries have restricted the Serb to only seven matches since his New York triumph on 13 September, but he believes he is "100% ready" for one last push.
"The shoulder is fine at the moment," said Djokovic, whose win-loss record for 2011 stands at 69-4. "I can say that it has recovered and I'm ready to compete.
"Everybody agrees that this tournament is the crown for all the achievements of the year for the top eight players in the world. I come here with high expectations."
Djokovic's season will go down as one of the greatest in history but, worryingly for his rivals, the 24-year-old Serb suggests he can perform even better in 2012.
"I know it's going to be a really great task to ask for but I have a lot of confidence," said Djokovic, who was unbeaten in a staggering 43 matches before losing to Federer at the French Open.
"It's always possible to get better. I like to think I have a complete game but I still have room for improvement."
ATP World Tour Finals order of play:
Sunday, 20 November: Federer v Tsonga (not before 1400 GMT), Nadal v Fish (not before 2000 GMT).
Monday, 21 November Murray v Ferrer (not before 1400 GMT), Djokovic v Berdych (not before 2000 GMT).