BERLIN (AFP) - Unseeded teenager Victoria Azarenka upset 15th seed Alona Bondarenko in straight sets to become the first player to reach the German Open semi-finals here on Friday.

Azarenka, from Belarus, 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.

She will now face either former world number one Serena Williams or Dinara Safina, who knocked out top seed Justine Henin on Thursday, in Saturday's semi-final.