(CNN) -- Novak Djokovic and Andy Murray were paired together in the same round robin group when the draw for the ATP World Tour Finals was made Saturday in London. 

With the exception of early exits in this week's Paris Masters, the pair have dominated men's tennis in the latter part of the season and join Tomas Berdych of the Czech Republic and Frenchman Jo-Wilfried Tsonga in a tough Group A for the end of season finale. 

Defending champion Roger Federer, who will officially lose his No.1 ranking to Djokovic Monday, heads Group B with fourth seed David Ferrer of Spain, Argentina's Juan Martin del Potro and Janko Tipsarevic of Serbia. 

The top two from each group qualify for the semifinal knockout stage at the O2 Arena. 

Murray, who followed up his Olympic gold medal in the singles with victory in the U.S. Open, where he beat Djokovic in an epic final, will play Berdych in his opener Monday. 

"There's always pressure at all of the major tournaments you play but I feel a little bit more relaxed coming in this year than I have in previous years because I managed to win the U.S. Open," he told Press Association. 

"But the only thing I can guarantee is that I'll give 110% on the court, fight as hard as I can until the end of all the matches and see where that gets me. Hopefully it'll get me a few wins." 

Murray last met Djokovic in another gripping final at the Shanghai Masters where the Serbian came out on top to boost his chances of regaining the No.1 spot from Wimbledon champion Federer. 
At which Arena?
t stage at the O2 Arena. 