Lindsay Davenport's hopes of winning back-to-back claycourt titles for the first time ended on Friday when she retired injured from her Family Circle Cup quarter-final against Justine Henin-Hardenne in Charleston, South Carolina.
The world number one had treatment to her right hip midway through the first set and, after Henin-Hardenne levelled, she quit when trailing 1-0 in the third set.
Davenport said she first felt the injury on Thursday night, and then aggravated it running for a ball in the second game of the match.
"I really felt it pull, and I got some additional taping to try and support it more, but it was hard to move," she said.
"I was trying to keep the points really short, but after a while you just can't play under 50 percent out there and it just was not going to happen.
In windy conditions, the Belgian broke early to lead 3-1 in the first set but Davenport held for 3-2, before reeling off the next four games to take the set despite receiving treatment following the fifth game.
As the match wore on, her movement became more hampered and once Henin-Hardenne had taken the second set and broken in the first game of the third, Davenport decided to quit.
Davenport said she hoped to be fit to lead the United States in their Fed Cup first-round match against Belgium in Delray Beach, Florida, next weekend.
"Something like muscle pulls, I tend to recover in like a week or so, so hopefully I'll be okay," she said.
Henin-Hardenne, in just her second tournament back after more than six months out through illness and injury, said she was delighted to be in the semi-finals.
"It's not the way I like to win, but I have to be positive," she said. "I'm in the semi-final, which is very good.
"Physically I am starting to feel better too, which is good because I played four matches here already, and I feel better day after day."
GOLOVIN AWAITS
Henin-Hardenne will meet Tatiana Golovin of France in the semi-finals after the 17-year-old continued her good run with a 7-5, 6-3 victory over seventh seed Nadia Petrova of Russia.
The 13th seed followed up her victory over defending champion Venus Williams with a rock-solid display from the baseline, forcing Petrova into a series of mistakes.
"This is the level where I want to be playing and where I want to be winning against these players," Golovin said.
"I want to be in the semis and the finals of these kind of big tournaments, and even bigger ones, like the [Grand] Slams."
Second seed Elena Dementieva sent down 17 double faults but still scrambled past Katarina Srebotnik of Slovenia 6-3, 5-7, 6-4 in a match containing 20 breaks of serve.
The Russian looked on her way out at 4-1 down in the third set but as Srebotnik tightened up, Dementieva battled back superbly to win five games in succession.
"At 4-1 down in the third set I was really ready, for the first time in my life, to give up and I could do it only because of the crowd support," Dementieva said.
"I was too negative today. The winds really affected my serve. I think it was really the most difficult conditions I've ever played in."
In the semi-finals, Dementieva will be looking for a revenge victory over eighth seeded Patty Schnyder after the Swiss ended the run of unseeded 15-year-old Czech Nicole Vaidisova 6-3, 6-2.
Schnyder came from 6-4, 4-0 down to beat Dementieva in the fourth round of the Australian Open in January.
"I've been waiting for this match," Dementieva said. "The last time we played I lost when I had a good chance and I would like to take my revenge."