Singapore (SportsNetwork.com) - In a battle of former world No. 1s, U.S. Open runner-up Caroline Wozniacki upset French Open champion Maria Sharapova in round-robin action at the season-ending $6.5 million WTA Finals.
The eighth-seeded Wozniacki outlasted the second-seeded Sharapova 7-6 (7-4), 6-7 (5-7), 6-2 in Tuesday's first match on the hardcourts at Singapore Indoor Stadium.
Sharapova captured the WTA Finals title in 2004 and is a two-time runner-up at the event, while Wozniacki was a finalist in Istanbul in 2010.
Another Day 2 result saw sixth-seeded Agnieszka Radwanska surprise third- seeded Wimbledon champ Petra Kvitova 6-2, 6-3.
Kvitova was the WTA Finals champ three years ago.
Wednesday's round-robin matches will pit current world No. 1 Serena Williams against fourth-seeded French Open runner-up Simona Halep and fifth-seeded Wimbledon runner-up Eugenie Bouchard versus seventh-seeded former top-ranked star Ana Ivanovic.
Williams has captured this prestigious eight-player tournament four times, including the last two years in Istanbul. The American great, who beat Li Na in last year's finale, is also a two-time Finals runner-up.
Williams (1-0) leads this week's four-player Red Group, which also features Halep (1-0), Bouchard (0-1) and Ivanovic (0-1). Sharapova (0-1) heads up the four-woman White Group, which also features Kvitova (0-1), Radwanska (1-0) and Wozniacki (1-0).
