The Danish player was trailing 2-4 in the first set when she slid for a drop shot and her foot caught on the clay surface. The No. 2 player was assisted to her chair and got her ankle taped.
To cheers from the crowd, Wozniacki returned to the court at Daniel Island. But after Zvonareva held to go up 5-2, Wozniacki double-faulted at 15-15 and retired. Wozniacki was looking for her second consecutive tournament win, after a victory last week at Ponte Verde Beach, Fla.
In today's final, Zvonareva will meet Samantha Stosur, who defeated Daniela Hantuchova 6-3, 7-6 (2).
Stosur, ranked No. 11, battled back after falling behind 5-2 in the second set.
Wozniacki, who was limping and had her ankle taped as she met with reporters, said she will have an MRI today. She said she heard a snap and felt pain while trying to run down the ball.
"I was surprised that I could stand on my leg, which was very positive, actually," she said. "But as soon as I was moving to the sides, it was impossible, so I couldn't play."
Wozniacki suffered a similar injury to her left ankle at Amelia Island two years ago that kept her away from tennis about three weeks.
She was asked if she will play the French Open, which starts the last week of May.
"Well, I certainly hope so. As it looks right now, it's not too bad," Wozniacki said.