EASTBOURNE (Reuters) - Australian Samantha Stosur became the first woman into the semi-finals at the Eastbourne International Open with a 7-6 6-4 defeat of Dane Caroline Wozniacki on Thursday.

Stosur, getting back into form after a long illness, will play eighth seed Nadia Petrova in Friday's semi-finals after the Russian beat compatriot Ekaterina Makarova 6-4 6-3.

All the players struggled with the windy conditions as Eastbourne's stiff sea breezes made serving difficult.

Doubles specialist Stosur, who had a second-round walkover when former Wimbledon champion Amelie Mauresmo pulled out of the grasscourt event with an injury, returned to tennis in April after seven months out with Lyme Disease and viral meningitis.

The former world number 27, now ranked 157 in the world in singles, was delighted to be back on form.

"I am very happy that I can get a result like this when I come back," the 24-year-old Australian said. "When you do step away for a long time and you can't do what you want to do I guess you certainly appreciate it more."

After an early exchange of breaks, Stosur won the first-set tiebreak 7-3.

The 17-year-old Wozniacki, who beat top seed Svetlana Kuznetsova in the second round here and was Wimbledon junior champion two years ago, failed to capitalise on three break points early in the second set.

Wozniacki, who twice exercised her right to consult her coach at changeovers, gave away a break point at 4-4 with a double fault. Stosur converted it with a backhand winner and served out for the match.

Petrova, playing with her right knee strapped, went 3-1 down at the start of her quarter-final against qualifier Makarova but pulled herself together and never looked back.

After getting an early break in the second set she broke again in the sixth game, helped by two double faults from Makarova who had beaten third seed Vera Zvonareva in the second round.

(Editing by Miles Evans and Padraic Halpin)