By Patrick Johnston
SINGAPORE (Reuters) - Caroline Wozniacki put a huge dent in Maria Sharapova's bid to finish the season as world number one by overcoming some distracting bright lights to down the Russian 7-6(4) 6-7(5) 6-2 in their marathon opening group match of the WTA Finals on Tuesday.
The Dane grabbed the final qualifying spot in the eight-woman field but it was world number two Sharapova who looked the lower ranked player at Singapore's Indoor Stadium, as some stunning winners were lost in a wave of 76 unforced errors.
The French Open champion also tossed in 15 double faults as she was broken seven times in an erratic display, with Wozniacki growing in confidence throughout the three hour 13 minute match as she sensed her opponent's struggles to find a fix.
The third game of a gripping White Group match encapsulated the night for Sharapova, as three perfect forehand winners put her 0-40 up on Wozniacki's serve, before she blasted balls low, wide or long to let the Dane off the hook.
That hold put the world number eight 3-0 up but the 27-year-old Sharapova showed all her champion spirit, as she fought back with some booming groundstrokes, breaking twice before serving for the opening set at 5-4.
The Russian, though, creaked under the pressure as two more double faults led to her being broken for 5-5 with more wobbles coming on her next service game where she saved a set point to force a tiebreak.
Sharapova led it 4-2 but once again creaked at the crucial moment, allowing the Dane to storm back with the next four points, before the Russian offered another double fault to gift-wrap the set 7-4.
Pumped up, Wozniacki broke in the first game of the second set but lost the advantage in the sixth game after becoming bothered by a light issue.
A flashing bulb stopped one point, with the Dane then unhappy about the brightness of some of the stadium's lights and demanding the chair umpire switch off the offending lamps.
Sharapova, nonplussed by the lights that continued to shine, broke back to level only to give back the advantage by losing her next service game to trail 5-3.
Wozniacki could not take advantage, though, as the Russian broke again and then looked liked grabbing the set before the Dane, infuriated by a bad line call, came off the ropes with some hard hitting to save a set point and force a second tiebreak.
Sharapova's inconsistent form continued though as she raced 3-0 ahead only to toss in more wild groundstrokes and allow her opponent to draw level at 3-3. Yet the Russian recovered her composure to edge it 7-5 on her second set point.
The duo traded early breaks in the deciding set before a tired-looking Sharapova folded as the match went into a third hour.
Wozniacki broke to lead 4-2, with Sharapova gifting another break and the match to her opponent when she sent a backhand long for yet another unforced error.
"In the third set I feel I stepped it up a little bit, went a bit more for my shots, I am happy to have won," a beaming Wozniacki said.
Sharapova can still finish the year as number one but must make it through to Sunday's final to stand any hope of overhauling Serena Williams, who began her Red Group campaign with a straight sets win over Ana Ivanovic on Monday.
Czech Petra Kvitova takes on Agnieszka Radwanska in the second White Group match later on Tuesday.
(Editing by Toby Davis)