World number one Maria Sharapova retired in the second set of her Pan Pacific Open semi-final against Serbia's Ana Ivanovic due to a hamstring injury.

Ivanovic will play second seed Martina Hingis in the final of the $1.3 million (661,000 pound) tournament after the Swiss beat Russian Elena Dementieva 6-4, 6-3.

Sharapova, trailing 1-6, 1-0, said she felt a sharp pain after serving in the second game of the first set, adding that she had been carrying a hamstring strain since the Australian Open.

"It's always difficult to end the tournament this way," the 19-year-old Russian told reporters. "I was hoping the pain would settle or get better, but against a top player it is hard to get away with not serving or returning well.

"My left hamstring has been having tightness since the Australian Open but after a grand slam you are tight all over," said Sharapova, who lost to Serena Williams in the Melbourne Park final last weekend.

"But this was a sudden sharper pain after I landed after the serve. I asked the trainer and she said these kind of strains take seven or 10 days to recover from, so hopefully I can recover quickly."

Hingis avenged her defeat by Dementieva in last year's final to stay on course for a record fifth Tokyo title.

"It was a great start for me today and I didn't really miss a shot," said Hingis, who raced into a 3-0 lead in the first set.

"I had a bad experience against her in last year's final and I was happy to get more than two games," said Hingis, who lost 6-2, 6-0 to Dementieva in 2006.

TRAINER CALLED

Fifth-seeded Ivanovic stormed into a one-set lead as an out-of-sorts Sharapova struggled on serve and the top seed called for her trainer at the end of the first set.

With on-court coaching allowed in Tokyo, Sharapova and coach Michael Joyce had a testy exchange with the umpire after the player was initially denied treatment for her injury.

An angry Sharapova, who won the tournament in 2005, demanded to see her trainer and Joyce accused the umpire of not knowing the rules. The trainer was eventually allowed on court.

A clearly limping Sharapova, who served 31 double faults in her previous two matches and four against Ivanovic, won her first service game of the second set before retiring.