Venus Williams's comeback from illness ended with a 6-4 6-1 defeat to Poland's Agnieszka Radwanska in the quarter-finals of theSony Ericsson Open on Wednesday.

For Williams, whose sister Serena was eliminated by Caroline Wozniacki on Tuesday, the defeat marked the end of her first singles tournament since last year's U.S. Open when she revealed she had been diagnosed with Sjogren's syndrome.

The auto-immune disease causes fatigue and joint soreness and, after doing well to reach the last eight by beating Ana Ivanovic, Williams looked tired in the latter stages of the 80-minute match

World number four Radwanska enjoyed a 74 percent first serve percentage while Williams, who entered the tournament as a wildcard, paid the price for 33 unforced errors.

The Pole, who won in Dubai in February, will face either top seed BelarusianVictoria Azarenka or France's Marion Bartoli who play their quarter-final later on Wednesday.