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Begu went down 5-2 in the third set against No.8 seed Galina Voskoboeva and was two points from elimination several times but managed to reel off five straight games for a 36 76(1) 75 triumph.
"At 2-5 I just decided to hold my serve and return every ball," Begu said. "It is very difficult to break Galina, but I did it twice and kept my nerves.
"Yesterday I played well to win against Cornet, and today against Galina was tougher. Galina is a good friend of mine and it's difficult to play her, but winning is always nice. I'm happy that I am playing well and my game is coming back."
Begu is into her third semifinal of the year after Acapulco and Palermo.
"I wanted to skip this event, but then I made up my mind to play just five days before and then applied for the visa and managed to get here," Begu said. "I came here without any pressures of rankings or points. My aim was to just get more matches in to improve my game and consistency and I'm happy that I have been able to do that in the last few days."
Next up for Begu is the only seed remaining, Urszula Radwanska. The second-seeded Pole also was pushed to the limit, letting a 5-3 third set lead slip away but eventually surviving seventh-seeded Alexandra Panova, 57 62 76(3). The three-hour, five-minute encounter is the tournament's longest so far.
"It was a great and close match," Radwanska said. "I tried to focus on every point and feel a little lucky to have pulled it out against a good friend. All credit to her for her play today."
Radwanska is no stranger to success here, as her semifinal showing last year was her best career result until she was runner-up at 's-Hertogenbosch in June.
Also terrific in Tashkent is Eva Birnerova, who despite coming into this week on a six-match WTA main draw skid, is now into the semis a year after making the final. She was a 63 46 62 winner over No.5 seed Alexandra Cadantu.
In Friday's final four, Birnerova will take on the surprise of the draw, Donna Vekic. The 16-year-old Croat qualified for her first WTA main draw this week and promptly has reeled off three straight wins without dropping a set, the latest being her 64 64 quarterfinal victory over sixth-seeded Bojana Jovanovski.
"Reaching the semifinals at a WTA tour event has not sunk in yet," Vekic said. "I went into the match with a lot of confidence. I went for every ball and am happy to have won against a Top 100 player for three days in a row now."
Vekic, the youngest player to make a WTA final four since 15-year-old Tamira Paszek was victorious at Portoroz in September 2006, talked about her transition to the pro tour.
"I stopped playing juniors after I lost in the junior quarterfinals at Wimbledon," Vekic said. "I decided that my junior tennis was over and decided to concentrate on the senior circuit. It is totally a different ballgame, but I have adjusted and feel comfortable on this level."