BIRMINGHAM (England) (AFP) Chinese top seed Li Na made it through to the semi-finals of the WTA grasscourt event here at Edgbaston after winning twice on Friday. Li first defeated German 13th seed Angelique Kerber, losing the first set but coming back to win 4-6, 6-3, 7-5 on a day when organisers tried to make-up for lost time in a rain-marred event. Her quarter-final opponent, Estonian Kaia Kanepi, wasted little time Friday in a 6-2, 6-2 victory over Portugals Michelle Larcher De Brito. Thoughts that Kanepi might be the fresher player were reinforced when she won the first three games against Li. But the 28-year-old Chinese regrouped. Li, the world number 12, won 6-4, 6-2 and will now face Frances Aravane Rezai in the semi-finals on Saturday. Earlier, second seed Maria Sharapova once again proved too strong for her old foe Sesil Karatantcheva as she reached the semi-finals with a 6-2, 6-4 win. Back in 2004, an altercation in practice at the Indian Wells event in the United States led to Karatantcheva vowing to kick her (Sharapovas) butt. But in front of a standing-room only crowd on one of the outer courts, Sharapova beat Karatantcheva in three sets, before thrashing her 6-0, 6-1 in the second round at Wimbledon a year later. Karatantcheva, the 2004 French Open junior champion, was banned as a 16-year-old for two years for a drugs offence in 2006. The Bulgarian-born player, who now represents Kazakhstan, has always maintained her innocence after testing positive for the steroid nandrolone. Second seed Sharapova won two matches on Thursday, com pleting a rain-delayed 6-0, 6-3 victory over Bethanie Mattek-Sands of the United States and then beating fellow Russian Alla Kudryavtseva 6-3, 6-1. The 22-year-old Sharapova, who recently returned to action after nine months out with a shoulder injury, told the BBC on Friday: I definitely feel in a better situation this year than last. Last year I wasnt sure how my arm was going to hold up, and I was always on the watch-out for that, but I feel much better about it now. Sharapova, Wimbledon champion in 2004, has won this Wimbledon warm-up event twice before and is seeded to meet Li in the final. But Sharapova must first get past Alison Riske in the last four. The US teenager arrived at Birmingham never having won a match on the main Womens Tennis Association (WTA) tour but she continued her fine form at Edgbaston with a three-set victory over world number 16 Yanina Wickmayer. Belgian third see Wickmayer won the first set on a tie break but a service break in each of the next two sets saw the 19-year-old Riske to a 6-7, (5/7) 6-4, 6-3 win. Regardless of the result of her match with Sharapova, Riske is sure to improve her career-high ranking of 185. Playing two matches in a day, as happened in several of Fridays quarter-finals, worked against Italian fifth seed Sara Errani. Having beaten Marina Erakovic of New Zealand in three sets in the morning, Errani was defeated in straight sets by fourth seed Rezai, with the Frenchwoman winning 7/6 (7/2), 7-5 in a close encounter.