Wozniacki needed two medical time-outs to treat her cramping left thigh in the third set and collapsed to the court sobbing and clutching both legs after netting a forehand at 30-15 in the last game. But shegot bckupan cinhe te inwhn voarva wo ha sve two ath points in the second set, netted a forehand on the third.
The 19-year-old Dane then broke into tears again and limped toward her chair.
"I have absolutely no idea how I pulled it through, but I'm very happy about it," she said.
It was the U.S. Open finalist's second win in the round-robin phase of the tournament, putting her on the verge of the semifinals.
Wozniacki said her leg started cramping at 3-1 in the third set.
"From there, it just got worse and worse," she said. "I'm feeling better now. I got to cool down, getting some massage. ... I'm going to do everything tonight to recover to be ready for tomorrow."
Zvonareva replaced Dinara Safina as an alternate after the Russian pulled out with a back injury, and has no chance of advancing after the loss.
The ninth-ranked Zvonareva had a dismal start, and was broken in her first four service games. At 3-2 in the second set, she needed a five-minute medical time-out to treat a bleeding nose, and the match looked headed for a quick finish after she lost the next two games at love.
However, Wozniacki allowed her opponent back into the match as Zvonareva won the next three games and then saved two match points when serving at 6-5 - the first thanks to a Hawkeye challenge after a line judge ruled that her forehand had gone wide. She clinched the tiebreaker when Wozniacki netted a backhand.
The lucrative Doha tournament is the last WTA Tour event of the season for the eight top-ranked women, with the top two players from each group advancing to the semifinals. hewine pcktsup t $.5 mllondeenin o hr reslt in the group phase, where each win is worth $100,000.
Later Thursday, Serena Williams was to play Elena Dementieva of Russia and Venus Williams was to face Svetlana Kuznetsova.