Good afternoon and welcome to LIVE game-by-game coverage of the first day of the 2015 Barclays ATP World Tour finals at the 02 Arena. First up in Group Stan Smith is world number one and reigning champion, Novak Djokovic against Japan's Kei Nishikori. The players are due on court shortly.

Can anyone stop Novak from landing a fourth world tour finals title in a row? Roger Federer will hope he is the man to do it. Join me again at 8pm GMT for coverage of his match with Tomas Berdych.

Novak is now receiving his end of year world number one trophy on court.... "It has been the most successful - and best - year of my life."

GAME, SET AND MATCH! - DJOKOVIC 6-1 6-1 NISHIKORI. A sensational volley into the corner is a fitting way to seal victory as Nole claims another break to secure a pair of breadsticks in a triumph that took just one hour and six minutes to construct. Kei was 30-0 up but lacked belief throughout and paid the price as Djokovic forced deuce before teeing up match point with a trademark sizzling return.

DJOKOVIC 6-1 5-1 NISHIKORI. Too good. Kei wins the first point but can do little to halt the Djoker juggernaut as the Serb rattles through the next four to move within one game of a routine success.

BREAK! - DJOKOVIC 6-1 4-1 NISHIKORI. It's all-but over. Nishikori crumbles as Nole hits back from 40-15 down to take four points in a row and claim the double break. A challenge at deuce proves crucial as Djoker's drive to the baseline was clearly in. Both players look bemused that the umpire didn't pick up on it. Kei tries to regain his focus but slams a weak two-handed backhand into the net to leave himself staring down the barrel of a crushing defeat.

DJOKOVIC 6-1 3-1 NISHIKORI. If you have chances against Nole, you simply have to take them. At 15-15 Kei has the opportunity to pass a winner down the line but crunches his attempt into the net. Djokovic responds with a sixth ace of the match and sees out the game 15.

DJOKOVIC 6-1 2-1 NISHIKORI. Cheers from what has been a subdued O2 crowd as Nishikori recovers from a double fault for 30-30 to take the next two points and keep alive his slim hopes of turning this around.

DJOKOVIC 6-1 2-0 NISHIKORI. Better from the Japanese. At 30-0 it looks like same old story but he battles back, engaging Djoker in some lovely exchanges. A sensational crosscourt forehand sends the world number one scampering and 'Special K' forces deuce by following up with a thumping winner into the open court. Ultimately it proves in vain as Nole consolidates the break as a challenge goes the way of the Serbinator to conclude one of the best games of this match so far.

BREAK! - DJOKOVIC 6-1 1-0 NISHIKORI. Another disaster for the Japanese as Nole takes a firm grip of the second set with an immediate break. It's something of a head scratcher for Kei. He's not alone in enduring this kind of conundrum against the world number one, not many have been able to challenge Djoker this season. He needs to find something from somewhere or this could end up as a real thrashing.

SET! - DJOKOVIC 6-1 NISHIKORI. Kei flashes another shot into the net and the opener is done and dusted in 32 minutes. Nole has been imperious and never looked like enduring any trouble with another easy hold to 15. What can Kei do to turn the tide here? Hard to see any way back for him.

BREAK! - DJOKOVIC 5-1 NISHIKORI. It's looking bleak for the Japanese. An attempted winner sizzles just long of the baseline and he finds himself facing double break point again. He's having no joy in the rallies so opts for an audacious dropshot from the back of the court that slams tamely into the net. Djoker to serve for the set.

DJOKOVIC 4-1 NISHIKORI. Another easy hold for Novak who has barely spent any time on serve compared to Kei. The Japanese isn't get much of a look-in and can muster just the one point as the Serb remains firmly in control.

DJOKOVIC 3-1 NISHIKORI. Kei gets on the board with a stubborn finale to his service game after it had threatened to slip away from him. At 30-0 and 40-30 he had his chances before an unfortunate net cord intervened and allowed Nole to force deuce and then notch up another break opportunity. The Japanese saved it with a stunning winner down the line and eventually came through to secure a hard-fought hold.

DJOKOVIC 3-0 NISHIKORI. No worries for the world number one as he proceeds to cruise through another service game to consolidate and put himself firmly in control here.

BREAK! - DJOKOVIC 2-0 NISHIKORI. A fine start just got better for the Serb. He piles pressure on the Japanese whose confidence will have taken a big hit after appearing to have saved himself from double break point down. Kei looked to have weathered the storm but couldn't get his nose over the finish line and in the end it was the Serbian who forced a skewed error from his opponent to claim an early advantage.

DJOKOVIC 1-0 NISHIKORI. An accomplished start for Nole offers an ominous warning of what might lie ahead for Kei. A pair of aces and some solid groundstrokes lead the world number one to a love hold.

Here we go... Djokovic will serve first.