BERLIN (AFP) - Giantkiller Dinara Safina took her second major scalp in two days as she sent former world number one Serena Williams out of the German Open just 24 hours after dispatching top seed Justine Henin. Having beaten neither Williams nor Henin before this week, the 22-year-old Russian, ranked 17th in the world, out-muscled Williams' power-game to book her place in the semi-finals with a dramatic 2-6, 6-1, 7-6 (7/5) win. She also ended Williams' 17-match unbeaten run after a tense two hours ten minutes battle and will play unseeded teenager Victoria Azarenka in Saturday's semi-final. Williams had beaten Safina in all their three previous meetings, having taken the first set 6-2 the American looked comfortable and there was little hint of the battle ahead. The Russian immediately responded by forcing Williams into a series of mistakes and kept the American pinned to the base line to romp into a 5-0 lead in the second set. Williams, ranked fifth in the world, started to show her frustration and although she picked up a game, Safina was not to be denied to take the second set 6-1.But with eight Grand Slam titles to her name, Williams knows what to do under pressure and a battle of wills emerged in the third set with neither side giving an inch. The set went to a tie-break and after a series of hard fought rallies, Safina earned two match points and held her nerve to claim victory. Earlier, Azarenka from Belarus upset 15th seed Alona Bondarenko in straight sets to become the first player to reach the German Open semi-finals. The teenager held her nerve to win the first set tie-breaker 7-2 and then had few problems as she took the second set 6-2. This was the 18-year-old's second win over seeded opponents in Berlin having beaten sixth-seeded Russian Anna Chakvetadze in the second round. Despite having never won a WTA tournament, Azarenka has contested two finals already this year on the Gold Coast and in Prague.