Miami - Poland's Agnieszka Radwanska brought Venus Williams's comeback event to a halt on Wednesday, downing the American 6-4, 6-1 to reach the semi-finals of the Miami hardcourt tennis tournament.
Radwanska, ranked fourth in the world, next faces either world no 1 Victoria Azarenka of Belarus or French seventh seed Marion Bartoli for a place in the final.
She needed 1 hour 21 minutes to overcome Williams, who was playing her first WTA tournament in more than six months after her abrupt withdrawal from the second round of the US Open, where she revealed she had been diagnosed with the auto-immune disorder Sjogren syndrome.
Williams, 31, is hoping to raise her world ranking high enough to allow her to compete at the London Olympics.
Currently 134th in the world, she is projected to move up to around 90th when the new rankings are released on Monday thanks to reaching the quarter-finals here.
The top 56 in the world as of early June are eligible for direct entry into the Olympic tournament, which will be held at Wimbledon.