The third round of the Madrid Open continued with Lucie Hradecka facing Ekaterina Makarova in the opening match.
Russia's Makarova had won both of their two previous meetings on court, but Hradecka got the better of the world number 41 in the opening set, taking it 6-2.
Makarova upped her game in the second set, which would be decided by a tiebreaker.
Hradecka of the Czech Republic edged it though - the world number 105 booking her quarter-final place with a 6-2, 7-6 (7-5) victory a day after knocking out defending champion Petra Kvitova.
Next up on centre court, a match-up between two former world number ones - Serena Williams taking on Caroline Wozniacki.
Denmark's Wozniacki had beaten Williams in straight sets in their only previous meeting this year in Miami and the number six seed was on top again on Thursday, taking the first set 6-1.
However, Williams bounced back from her poor start to the match and having already broken to lead 3-2, the American picked apart Wozniacki's serve again in the ninth game to take the set 6-3.
Williams broke 2009 Madrid runner-up Wozniacki in her first service game in the third set and never looked back.
Serving to stay in the match at 5-2 down, Wozniacki saved one match point, but Williams wrapped up the win moments later with a backhand.
The number nine seed hit 43 winners in all on the way to a 1-6, 6-3, 6-2 victory.
That result saw Williams improve her record against Wozniacki to four wins and three defeats and she also advanced to the last eight in Madrid for the first time in her prestigious career.
SNTV