Good afternoon everyone and welcome to live game-by-game updates as Roger Federer takes on Jo-Wilfried Tsonga in the opening game of the World Tour Championships in London!

We'll be back at 20:00 GMT for the second match, as Rafa Nadal takes on Mardy Fish. In the meantime, you can join me, Mark Patterson, on Twitter to discuss the match

What a terrific contest that was - ebbed and flowed over the course of three sets. Both players can take heart, but it's Federer who takes the win. Tsonga now probably needs wins against both Nadal and Fish to advance.

FEDERER 6-2 2-6 6-4 - WINNER! Careless start - Tsonga hits a high volley low into the net - and then his second serve is punished to let Federer in at 0-30. Federer senses a chance, and steers a forehand down the line from mid-court to bring up three match points! Tsonga denies him the first, but the Swiss does it at the second opportunity! Backhand behind Tsonga, and Federer's 13-match winning streak continues!

FEDERER 6-2 2-6 5-4 - Tsonga lingers in a couple of rallies, but is no danger at all to Federer in this game. An equally authorative hold to love. You'd think this has tie-breaker written all over it, but with Tsonga now serving to stay in the match, strange things can happen...

FEDERER 6-2 2-6 4-4 - Terrific serving from Tsonga, including a cracker of an ace down the line. Federer didn't get a ball back in court. Over to you, Roger.

FEDERER 6-2 2-6 4-3 - The Swiss not looking tired, Tsonga mopping his brow. No surprise, perhaps, the way Fed sends JWT around the court in another relatively simple service hold. Just the one point for Tsonga as Fed nudges closer to the finish line.

FEDERER 6-2 2-6 3-3 - Tsonga just looks a little shaky as we reach the mid-point of the deciding set. Federer drags the score back to 30-30 with a passing backhand which might just be the shot of the match, then forces an error to bring up a break point - brave shot from Tsonga wrongfoots him to get us back to deuce. 137mph service winner down the line for advantage, and Tsonga holds. Any closer to picking a winner?

FEDERER 6-2 2-6 3-2 - Having said Tsonga was having marginally the easier time of things on his serve, Federer, seeded fourth here in London, eases through the first three points in double-quick time. He puts a backhand long, but it only delays the inevitable hold of serve.

FEDERER 6-2 2-6 2-2 - Tsonga holds again to level things up. There's so little to separate these two at the moment. If anything, the Frenchman is having the easier time on his serve, but you wouldn't back against a tie-break at this rate.

FEDERER 6-2 2-6 2-1 - Federer a little lucky there as Tsonga blows a forehand which would have given him a 15-30 lead. Federer moves to game point before JWT cuts off a lob with a superb volley at full stretch. Federer then sends a volley wide to give the Frenchman a sniff at deuce. This time, though, the Swiss has enough to hold him off. Still on serve.

FEDERER 6-2 2-6 1-1 - Another point that has the crowd off their seats - Federer and Tsonga trade blows at the net, only for the Frenchman to find a putaway shot that looked all too easy. But he makes a mess of his forehand on the next point to allow Federer back to 30-30. Half a chance for the Swiss? If it was, it's shut down quickly as Tsonga holds.

FEDERER 6-2 2-6 1-0 - Federer almost ludicrously unflappable. Just been soundly beaten in the second set, but his facial expression doesn't alter at all. He sends down some excellent serves to get on the board with a hold to 15.

FEDERER 6-2 2-6 - SET! Tennis does this sometimes. Federer looked untouchable in the opening stages, but now all of a sudden he looks like a man with no answers. Twice in a row Tsonga ends rallies with obscene drop shots, the sort you'd scarcely dare to try. Federer reminds us of his capability with a passing winner on the forehand, but Tsonga rattles off the next two points to set up a final set shoot-out!

FEDERER 6-2 2-5 - BREAK! Federer nudges ahead with two tasty backhands - we've not seen too many of those today from Federer. Tsonga responds - return down the line too good, and it's 30-30. Tsonga unleashes a brilliant backhand of his own to force deuce - the first of the day. Federer can't close it out, and Tsonga with some vicious groundstrokes manages to break!

FEDERER 6-2 2-4 - Lovely first point goes the way of the Frenchman when he plays a touch volley off his backhand at the net. Tsonga looks to have the momentum, only to throw in a double fault. This time it doesn't cost him, and JWT maintains his advantage.

FEDERER 6-2 2-3 - Tsonga had done all the hard work to take a 15-30 advantage, only to blow a simple forehand to finish it off. That makes it 30-15 for Federer, and it's just what the Swiss needs to stop the slump. Two perfectly-placed serves, and he seals a hold of serve.

FEDERER 6-2 1-3 - Tsonga up into a 30-0 lead as Federer can't quite thread a passing shot down the byline. Tsonga wraps up a hold to love with a service winner past the backhand - that means he's won more points in this set already than he managed in all of the first.

Federer had dropped three points in the whole of the first set, then gave up four in a row to basic errors. What happened there? It's what the match needed, though.

FEDERER 6-2 1-2 - BREAK! Your eyes don't deceive you - Federer drops a point on his serve as a sliced backhand dips too late to catch the back line. That drags Tsonga back to 30-15, and a backhand into the net from the Swiss makes it 30-30. Then a shocker - Federer beats Tsonga with a serve to the body, only to blow his putaway at the net. Tsonga's first break point chance - and he takes it because Federer makes another inexplicable error on the forehand!

FEDERER 6-2 1-1 - Well done JWT - powerful serving, a couple of confident forehand putaways, and a delightful forehand from the back of the court. He keeps it on serve. Last serve measured at 137mph, by the way. Nippy.