Holder Kvitova shocked, Sharapova and Serena win in Istanbul
Agnieszka Radwanska beat faltering defending champion Petra Kvitova while Serena Williams and Maria Sharapova also won on the first day of the WTA Championships in Istanbul.
Powerful Czech Kvitova committed a multitude of unforced errors and six double faults while Pole Radwanska defended dutifully and found some lovely shots of her own to claim the match 6-3 6-2.
It was a slow start from Kvitova, ranked sixth in the world, as she fell three games and a break down. Yet in amongst the wide forehands there were some decisive winners, and you felt that she could get into the swing of the match at any moment.
Having saved three break points in the fourth game she attacked the Radwanska serve and claimed the break back with ease. A hold followed for 3-3 as both players exhibited a sea change in confidence.
Yet that surge of belief came crashing down as some savvy shot-making from Radwanska put her back ahead. Kvitova was soon a break down again as she lost her range and barely offered any resistance as the world number four sealed the set with a hold.
Kvitova had won all three of their previous meetings, including in the round robin of last year's WTA Championships. Yet Radwanska made it four games in a row with an immediate break at the start of the second set. Kvitova got only 59 per cent of her first serves in compared with the 71 of her rival.
Breaks followed in each of the following two games, with Radwanska committing uncharacteristic errors on her serve before Kvitova failed to capitalise, notably committing two doubles in a row to concede the momentum again.
Radwanska calmed the waters with a love game to hold for 3-1 before breaking again as Kvitova smashed into the net from close in.
However Kvitova - who was 25-0 on indoor hardcourts since the start of 2011 prior to the match - suddenly thrived again to grab one break back and remain in contention as she sought to attack the net.
Once more it was a false dawn as Kvitova fired a forehand wide - the chief sin of her match - to give her opponent two break chances. On the first, Radwanska gallantly chased balls sent deep yet should have lost the point as Kvitova came close - and fired her forehand well out.
Radwanska completed an excellent first day's work in Turkey in the following game, serving her third ace on her third match point to seal it.
"It was a little bit different, but the nerves were there for sure," Kvitova said. "I was nervous all the match. I felt my fingers weren't still moving and I didn't move on my legs. I'm disappointed in myself.
"I had a lot of errors and it wasn't good tennis from my side... If you are not playing like some matches before and now you have a player who's number four in the world, it's not easy to be relaxed."
Kvitova is seeking to become the first player to win back-to-back WTA Championships since Justine Henin in 2006-07 - but on this evidence she will struggle to do so.
Williams began her campaign with a 6-4 6-1 win over Angelique Kerber.
Playing in her first tournament since winning the US Open in August, third seed Williams's greater serve and power were too much for WTA Championships debutant Kerber.
The American started strongly, moving three games up in short order, while Kerber had to battle desperately to save the fourth and avoid going double break down.
Kerber, anxious and overly aggressive from the off, took that fledgling momentum and turned it into a break back, successfully challenging a Williams winner on the sideline on the last point - the ball had landed millimetres out.
With a more cohesive gameplan, Kerber matched Williams hold for hold until, at 5-4 down, the German committed a double fault on game point. Serena, controlling from the centre of the baseline, took advantage of that reprieve to break for the set.
The only game won by Kerber in the second stanza made it 1-1. It was a love game, but her serve looked suspect even then.
Her confidence was cracked when, having taken Williams to deuce in the next game, she played a beautiful drop shot only for the 15-times Grand Slam champion to flick it expertly down the line then smash the looping defensive shot that came back to hold.
Kerber did not roll over, offering resistance in each of the following games, but ultimately Williams's domination of the points proved too much.
It was the first match world number five Kerber had lost to a Williams sister this year, having beaten Serena once and Venus three times.
"I felt like I was ready to play," Williams said. "I felt like I practised too much, and if I hit another practice ball I'm going to go nuts. So I just really wanted a match.
"I was like, if I have another practice day, I don't know if I can handle it."
Sharapova opened her campaign with a repeat of her 6-3 6-2 victory over Sara Errani in the French Open final after overcoming tough resistance in the early games of the opening set.
The champion of eight years ago had to withstand some typically dogged early defending from the lightning fast Errani, as some incredible retrieving got her back on level terms at 2-2 in response to Sharapova’s early break, much to the Russian’s bewilderment.
But from 2-2, Sharapova's groundstokes nullified Errani’s court coverage and the Italian was broken again in the sixth game before Sharapova served out to take the opener 6-3.
Her tail well and truly up, Sharapova continued where she left off at the start of the second set, blazing winners to break to love. Errani looked broken herself and a stunning backhand winner gave Sharapova an unbreakable grip on the match with a second break in the fifth game of the second set.
Although Errani dug deep to make her serve it out, Sharapova completed her 49th win out of 50 matches in 2012 after being a set up.
Sharapova, currently ranked second behind Victoria Azarenka, must win at least two of her group matches before winning the title to have a chance of ending the year as the number one player.