Mason (Ohio), Aug 17: Tenth-seeded Mardy Fish reached the quarterfinals of the Western & Southern Open with a 6-3, 6-3 win over Radek Stepanek on Thursday.
Women's top seed Agnieszka Radwanska overcame an unexpected challenge from wild-card Sloane Stephens before prevailing 6-1, 4-6, 6-4. Radwanska reached the quarterfinals for the first time in three appearances at the $5.7 million event.
Fish, a two-time runner-up at this event, beat his Czech Republic opponent for the first time in five career matches, including three straight-set losses.
Fish celebrated his win with a leaping right fist pump after Stepanek's backhanded drop shot hit the net on match point.
The American hasn't dropped a set and has been broken only once while rolling into the quarterfinals.
Men's sixth-seed Juan Martin Del Potro also was tested before finally pulling away in the third set for a 7-6 (2), 2-6, 6-1 win over Viktor Troicki of Serbia. The Argentinian improved to 6-0 in his career against Troicki.
Germany's Angelique Kerber became the first player to reach the quarterfinals. The No. 5 seed needed to win a tiebreaker to advance with a 6-4, 7-6 (5) win over qualifier Andrea Hlavackova of the Czech Republic.