Welcome to coverage of Serena Williams's first match at the WTA Championships in Istanbul against Angelique Kerber.

Up next: Maria Sharapova v Sara Errani.

What did you think of that match? Is Serena looking at a third WTA Champs title?

WILLIAMS 6-4 6-1 KERBER - GAME, SET AND MATCH - After new balls are introduced for this game, Serena saves break point with a cracking shot and seems intent on completing the job here. She does so when Kerber hits wide.

WILLIAMS 6-4 5-1 KERBER - BREAK - Serena one game from victory after triumphing from deuce thanks in part to a stunning driven winner. Kerber falls short when it really matters.

WILLIAMS 6-4 4-1 KERBER - Serena sends a drive volley home for 30-15 when Kerber's return comes back and goes on to seal the hold and close on victory.

You can watch all the action from the WTA Championships in Istanbul on British Eurosport or online.

WILLIAMS 6-4 3-1 KERBER - BREAK - Kerber, who has played more matches than anyone on the WTA this year - this is her 80th - serves a double fault and two unforced errors follow to put her 0-40 down. Serena plays a backhand into open court to make the most of the second of them.

WILLIAMS 6-4 2-1 KERBER - Kerber, who is 4-0 against the Williams sisters this year (1-0 against Serena, 3-0 against Venus), unlucky to see a fierce shot down the line strike the net. She takes Serena to deuce but finds the net again... Serena then races to meet a drop shot, flicks it expertly down the line and smashes the looping defensive shot that comes back. Top tennis. Is she the best ever?

WILLIAMS 6-4 1-1 KERBER - Kerber struggling to get her first serve in but takes a love game nevertheless as she fires down winners from the baseline. She refuses to be swept away in this match.

WILLIAMS 6-4 1-0 KERBER - Kerber doesn't offer up a great deal of resistance as Serena moves ahead in the second set.

WILLIAMS 6-4 KERBER - SET - Kerber commits a double fault on game point to let Serena back into it and she punishes her by breaking for the set. Powerful shot-making from the baseline from the 15-times Grand Slam champion.

Serena's beau (and coach) Patrick Mouratoglou looking relaxed courtside. The Eurosport blogger had his say on her in May - perhaps she read his view that "Serena isn't just another player, or even another champion, but the best player this century" and asked him to dinner...

WILLIAMS 5-4 KERBER - Williams struggling to put Kerber away, but only because the latter reads the attacking shots so well and defends them. However Serena takes a love game nonetheless. The American has won 43 of her last 45 matches - one of those two losses came against Kerber in the quarter-finals of WTA Cincinnati.

WILLIAMS 4-4 KERBER - Kerber looking good now, hitting well as she sends an excellent forehand winner to the corner. Serena seeks to save game point with a net approach but her backhand volley is into the net - good passing attempt by the German.

WILLIAMS 4-3 KERBER - Serena dominates this game from the centre of the baseline to take it without losing a point. She is looking to get back into her zone as she hasn't played since the US Open.

You can watch all the action from the WTA Championships in Istanbul on British Eurosport or online.

WILLIAMS 3-3 KERBER - Kerber focuses on getting the ball back to her more illustrious rival after an aggressive start that put her 3-0 down. Serena does come back to 40-30 after going 40-0 behind, but the game is Kerber's. /// @AntonClarke1: "If Serena Williams is fit and healthy she beats everyone else with ease. Its that simple!"

WILLIAMS 3-2 KERBER - BREAK - Kerber back on serve! She takes the fight to Serena to go 30-40 up only to see the latter beat her with a shot on the sideline. Kerber challenges - and the ball in fact landed about a millimetre out! Great challenge.

WILLIAMS 3-1 KERBER - German Kerber on the board but boy does she have to fight for it... she throws herself into her shots from the baseline as she fights her way to 40-30 up but finds the net for deuce. Serena saves a few game points but finally succumbs.

WILLIAMS 3-0 KERBER - Serena is ranked three and Kerber five, the latter's ranking this week her best ever. Williams coming close to the net at the slightest opportunity to attack and takes a love game to lead by three games.