Brisbane - Top seed Samantha Stosur has been knocked out of the Brisbane International after a 6-4 6-2 loss at the hands of Iveta Benesova of the Czech Republic on Wednesday.
The US Open champion was unable to handle the lefthander, who attacked the Australian's backhand throughout the match to force errors, and lost in 70 minutes.
It was the second successive year the world number six has been the top seed at Brisbane and lost in the second round. Last year, she lost to compatriot Jarmila Gajdosova.
Benesova, who had never beaten Stosur in their previous four meetings, will now meet Australian Open champion Kim Clijsters in the quarter-finals.
Men's second seed Gilles Simon, however, had no such problems, dispatching Australia's James Duckworth 6-3 7-5 to move on to the quarter-finals.
The Frenchman joins Uzbekistan's Denis Istomin in the last eight, after he advanced courtesy of a walkover following Tommy Haas's withdrawal with a calf injury.Results from the fourth day of the Brisbane International at the Queensland Tennis Centre on Wednesday (x denotes seeding):
Marcos Baghdatis (CYP) bt Kei Nishikori (JPN x5) 6-3, 6-4
Bernard Tomic (AUS x8) bt Tatsumo Ito (JPN) 6-1, 6-2
Alexandr Dolgopolov (UKR x3) bt Igor Andreev (RUS) 6-7 (3/7), 7-6 (11/9), 6-2
Santiago Giraldo (COL) bt Philipp Petzschner (GER) 6-4, 6-4
Gilles Simon (FRA x2) bt James Duckworth (AUS) 6-3, 7-5
Radek Stepanek (CZE x6) bt Jarkko Nieminen (FIN) 7-6 (7/3), 6-2
Serena Williams (USA x4) bt Bojana Jovanovski (SRB) 6-2, 6-4
Jelena Jankovic (SRB x6) bt Nina Bratchikova (RUS) 6-3, 6-2
Iveta Benesova (CZE) bt Samantha Stosur (AUS x1) 6-4, 6-2
Kaia Kinepi (EST) bt Anastasia Pavlyuchenkova (RUS x7) 6-0, 6-3