Three holds of serve put the Dane ahead at 4-2. Williams, still not playing at full speed,
had however managed to strike an ace down the tee on gamepoint in both of her service games.
With Wozniacki serving ahead 4-2, Williams netted a forehand down the line as well as a crosscourt backhand as the Dane held at love for 5-2.
Disappointed with her current form, Williams smashed her tennis racket on the court causing the frame to break into several parts which resulted in a warning from the chair umpire for racket abuse.
Serving to stay in the set, Williams netted a backhand down the line then struck a crosscourt forehand wide to trail 0-30 before Wozniacki hit an inside out crosscourt backhand return winner to set up set point.
Williams saved the first set point with an ace out wide before striking a crosscourt forehand wide to trail 2-6.
Wozniacki held serve to lead 1-0 in set two before Williams turned up the pace and volume on her groundstrokes.
Striking the ball early, extremely hard and with a loud grunt each time, Williams struck two swing volley winners and an ace out wide before holding serve at love in a pivital service game to draw even at 1 all.
Wozniacki held serve to lead 2-1 before Williams won three games in a row to lead 4-2.
With Wozniacki serving to stay in the set down 3-5 30 all, Williams struck an inside out crosscourt backhand return winner to reach set point.
A double fault from the Dane leveled the match at one set all.
Serving down 1-2 30-40 in the final set, Wozniacki won a 26 stroke rally after Williams hit a crosscourt forehand wide which drew applause from Williamsí mother Oracene.
The set remained on serve with the score leveled at 4 games all.
With Williams serving at deuce, Wozniacki struck a backhand down the line return winner before the American netted a down the line backhand to drop serve and trail 4-5.
However Williams then struck three forehand winners followed by an overhead winner to break serve to reach 5 all before holding serve to lead 6-5.
Serving to stay in the match, Wozniacki fought off a match point with a down the line forehand volley winner before holding serve to reach a decisive tiebreaker.
Williams, who had been 7-0 in tiebreakers this year, quickly fell behind 1-4 following several groundstroke errors and her second double-fault of the match.
However the American then won five points in a row after hitting several extremely powerful shots including a 124.9 miles per hour serve.
With Williams ahead 6-4, the Dane saved two additional matchpoints following two Williams forehand errors.
At 6 all, Williams struck an ace out wide to set up a final matchpoint.
Williams struck a powerful forehand down the line return which Wozniacki returned with a forehand down the line wide to end the match after two hours and 13 minutes of play.
Williams, who started the day slowly, finished on a high with 50 total winners including 12 aces.
In Sundayís final round match at 7:00pm Singapore time (4:00am PST USA), Williams gets a rematch versus the fourth seeded Simona Halep of Romania.
Earlier this week in round robin play, Halep defeated Williams 6-0, 6-2 in one of the Americanís worst losses ever.