World number one Maria Sharapova failed to celebrate her return to the top of the rankings after she abandoned her semi-final match in the Pan Pacific Open on Saturday.
After losing the first set 1-6 to Ana Ivanovic of Serbia, the Russian top seed, 19, received court-side treatment to her left thigh but failed to recover, giving up after winning the first game of the second set.
In the final Sunday, Ivanovic will face former world number one and second seed Martina Hingis of Switzerland, who avenged her loss in last year's final to Elena Dementieva of Russia with a 6-4, 6-3 win.
"This is something that I've had for a week or so now. After the second game, I felt a much sharper pain," said Sharapova.
"It's always disappointing to end a tournament that way," she added. "I definitely tried to find the way, hoping the pain was settled and (would) get better. That's why I tried to play the first set."
Fifth-seeded Ivanovic, who had beaten her compatriot and fourth seed Jelena Jankovic in three sets on Friday, said it was not a good way to win a match.
"From the beginning of the match, I didn't notice anything, because she was moving pretty well and also serving OK," said the Serbian, also 19.
"I was really surprised that at the end of the set she called a physician and straight away retired. It was surprising that she had a problem."
Ivanovic added: "It's never nice to win the match that way. I felt pretty confident and I was happy that each match I played better and my serve was working really well -- that's very important to play against top players.
"I also think I was moving pretty well on the court and I was very aggressive, which is very important to play against Maria, not to give any time, and I was pretty happy with my performance today," she said.