Monica Niculescu broke Caroline Wozniacki's serve when the No. 1 seed was serving for the match at 5-1, but Wozniacki had already put too many games between them.
Wozniacki had 23 winners and three aces in her third round victory.
The No. 1 seed defeated Niculescu 6-2, 6-2. The match took one hour and 16 minutes.
Only four rounds stand between the 21-year-old from Denmark and a tournament title, something that has avoided her since she made headlines from her sneakers to her play in the 2009 U.S. Open.
Wozniacki will play the winner of the third-round match between Christina McHale of America and Jelena Jankovic of Serbia. Jankovic is the tournament's No. 13 seed.
Wozniacki last met Jankovic in a major in the fourth round of the 2008 U.S. Open. Jankovic walked away the winner after three sets, 3-6 6-2 6-1.
Wozniacki and McHale have never gone head-to-head in a Grand Slam. They have only played two times during WTA events, winning one meeting a piece. Both of those tournaments were hard court.