Good afternoon and welcome to game-by-game coverage of the ATP World Tour Finals Group A encounter between Marin Cilic and Tomas Berdych. The players are due on court around 2pm GMT.

GAME, SET AND MATCH! - CILIC 3-6 1-6 BERDYCH - There's a chink of light for Cilic as he works his way to two break points, only to see his hopes dashed by some brave play by Berdych. The Czech makes hard work of it but finally serves it out. The result means Berdych keeps his hopes of a semi-final berth alive with a comprehensive triumph while Cilic, who has endured a real nightmare on his first appearance at the end of season tournament, needs a minor miracle to progress with two defeats from two matches.

BREAK! - CILIC 3-6 1-5 BERDYCH - A stunning return winner down the line gets Berdych off to a flyer and Cilic follows it up with a misguided drop shot into the net cord. The Czech takes advantage to notch up three break points with a simple shot past a static Cilic at the net. The Croatian manages to save one but can't prevent the inevitable. Berdych will now serve for the match.

CILIC 3-6 1-4 BERDYCH - It's definitely one of those days for Cilic as he decides to challenge midway through a rally he is dictating. The ruling goes against him and eventually loses the game to 30 as Berdych blasts down a big serve to seal it. There's a shake of the head from his coach Goran Ivanisevic who has the look of man who believes defeat is now inevitable.

BREAK! - CILIC 3-6 1-3 BERDYCH - The aces have been few and far between for Cilic so far today but he pulls a pair out of the hat to lead 30-0. There appears to be no danger, but Berdych hits back and wins a superb rally to turn the game on its head before teeing up break point with a backhand winner. Cilic needs to dig deep but instead buckles with a wild shot that flies way out of court. Berdych is well and truly in the driving seat now.

CILIC 3-6 1-2 BERDYCH - Berdych uses his third ace of the match as a 'get out of jail free card' to force deuce and go on to seal the game after Cilic had threatened the break at 15-40. Marin will look back on that one ruefully after sweeping a second serve return that had looked simple enough, way long of the baseline.

CILIC 3-6 1-1 BERDYCH - The Croatian speeds into a 40-0 lead but suffers a wobble as a volley into the net and a wide backhand see Berdych reduce the arrears. It's a test of the US Open champion's nerve but he comes through it with a trusty big serve to level it up.

CILIC 3-6 0-1 BERDYCH - Ominous signs for Cilic as Berdych rampages through an easy opening service game of set two. The Czech's belief is on the rise while Cilic still appears to be battling those inner demons.

SET! - CILIC 3-6 BERDYCH - The Birdman claims the opener with a second break of serve to brush aside a misfiring Cilic in just over 40 minutes. The Czech needs two bites of the cherry, however, after a lovely backhand winner was followed by a poor forehand that he hurriedly snatched at to take it to deuce. But Cilic's lack of consistency again proves decisive as his shot into the corner narrowly misses the line to hand his opponent the set.

CILIC 3-5 BERDYCH - A decent chance goes begging for the US Open champion as Berdych moves to within a game of the set. It had looked like a change of momentum was on the cards, as a brace of blistering forehands from Cilic led to an emphatic overhead winner before a crisp volley into the corner from the net gave the revitalised Croat two break points. Berdych retorted with a quite sublime crosscourt winner and Cilic then handed him the reprieve with a drive that flew long of the baseline. The Czech seized his opening with both hands as he came up trumps following some blazing rallies to hold.

CILIC 3-4 BERDYCH - Berdych gets the scent of a double break as Cilic continues to labour. At 15-40 it's looking ominous but a lung-bursting rally ends with the Czech's attempt down the line lashing into the net. It gives Cilic a glimmer of hope and he roars back to pull off a major hold that he celebrates with the obligatory fist pump. A missed opportunity for Berdych - will he live to regret it?

CILIC 2-4 BERDYCH - It's more accomplished play by the Birdman as he continues to rain down the bullets, coming into the net at the right moments to keep Cilic guessing. It's another love hold, making it 11 points in a row for the Czech on serve. Cilic is going to have to find a way of making some inroads sooner rather than later or this set is only going to go one way.

CILIC 2-3 BERDYCH - It's still a bit ragged from Cilic but he finds some sort of rhythm at 15-30 to surge back and wrap up the next three points. He remains just the one break behind but is still missing the spark that could yet ignite his tournament.

CILIC 1-3 BERDYCH - A combination of hefty first serves and some wild miscues from Cilic allow Berdych to almost saunter into a 40-0 lead and he confirms the perfect hold with a confident overhead at the second time of asking.

CILIC 1-2 BERDYCH - That's more like what we've come to expect from Cilic as he eases to a love hold with some trademark big serving. It will do his confidence the world of good as both players appear to have settled into the contest. That's two quick-fire games after a lengthy eight-minute opener.

CILIC 0-2 BERDYCH - Berdych's wide serve and shot down the line tactic snaps into the net to hand Cilic an Opportunity Point (OP) at 15-30. But it proves a false dawn as the Czech sizzles down some huge serves to hit back and consolidate the break.

BREAK! - CILIC 0-1 BERDYCH - The nightmare continues for the US Open champion who just can't seem to get going in London. A sloppy start sees him rack up a trio of tame, unforced errors to hand the Birdman a huge opportunity. The Croatian claws two back before thumping down a big serve to force deuce. The pair trade blows until Berdych's deep shot and approach to the net snare a fourth break chance and this time he takes it, teasing out the error into the net from Cilic with a rasping crosscourt effort.

Here we go, Cilic to serve first...

As for Berdych, the Czech pulled no punches in his appraisal of his loss to Wawrinka. He said: "Unfortunately, it was my worst match of the whole season and I kept it for the start here. I didn’t really feel anything right. I can just keep fighting and try to play good tennis.”

Cilic on his defeat to Djokovic: "I felt that Novak played really, really solid. I felt a little bit uncomfortable on the court, rusty… I was not hitting it clean. That’s always difficult, especially against Novak, to get away with a win when you’re not playing so good.”

The players have arrived on court and we are just moments away from what is almost certainly a win or bust contest for both of them.