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, 6-7, 6-2 in their marathon opening group match of the WTA Finals.
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.
"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.