Updated

By Simon Evans

MASON, Ohio (Reuters) - A tearful Ana Ivanovic was forced to retire with a foot injury early in the first set of her semi-final against Kim Clijsters at the Cincinnati Open on Saturday allowing her Belgian rival to go through to the final.

After receiving extensive treatment she came back to court but was clearly in pain and had to retire. The set stood at 2-1 for Clijsters who had broken Ivanovic's second service game.

Clijsters will face the winner of the all-Russian semi-final between Maria Sharapova and Anastasia Pavlyuchenkova.

It was a huge disappointment for former world number one Ivanovic. Trying to claw her way back up the rankings, she had looked in good form during the week, reaching her second semi-final of the year.

"I'm obviously disappointed the way it finished because I felt like I had really good run," said Ivanovic.

"Just on that one forehand when I went to step around it, I just felt so much pain in my foot and I couldn't step on it anymore.

"I tried bit of tape, but I could not put any weight on it and there was no point in me continuing."

The Serb said the injury was not a recurrence of any previous problem. "I was very scared and it was painful."

Clijsters, the defending U.S. Open champion, said she hoped the injury healed quickly.

"She is doing well again and then something like this happens, I hope she is OK and it is nothing too serious and she will be OK for the U.S. Open," she said.

The first round of the U.S. Open begins on August 30.

(Reporting by Simon Evans; Editing by Tom Pilcher)