MADRID, Spain - No.11 seed Caroline Wozniacki's Mutua Madrid Open campaign ended prematurely due to injury on Sunday.
The former World No.1 completed just three games against France's Alizé Cornet before retiring with a lower back injury and the Frenchwoman leading, 3-0.
Wozniacki received a medical timeout at the first changeover, and also arrived on-court with wrapping on her left leg.
"It was still the very beginning of the match, so anything could happen if she wasn't injured. I don't consider it like a real win over Caroline," Cornet said.
"We used to have such big fights in the past, in three sets, playing three hours. Today, I'm very sorry for her that she feels her back is painful. I know how it feels, and I know it's bad, and I just hope that she's going to get well very soon."
Wozniacki was making her first appearance in a WTA event since finishing runner-up to Madison Keys at the Volvo Car Open in Charleston in April.
Cornet advances to the second round of the Premier Mandatory event for the fourth time in her career, where she will face China's Zheng Saisai, who defeated compatriot Wang Yafan, 7-5, 7-6(3) earlier on Sunday.
"I know her, but I haven't played against her, so it's going to be the very first time," Cornet said.
"I hope I'm going to be playing as I was playing in the beginning of this match - very well, and putting a lot of intensity. I'm going to try to get to the third round for the first time in my life in Madrid."