World No . 1 Nadal , riding a 12-match winning streak on hard courts , will face Roger Federer in Friday 's marquee encounter . Novak Djokovic will enter this year 's Romania Open without a title since Friday . Serena Williams loses to big-serving American John Isner at the Cincinnati Masters on year . Andy Murray also exits in the quarterfinals following a defeat to Czech Tomas Berdych . Serena Williams reaches the semifinals by ousting Cincinnati 's Simona Halep .
World No . 1 Novak Djokovic will enter this year 's Romania Open without a title since Friday . Serena Williams loses to big-serving American John Isner at the Cincinnati Masters on year . Andy Murray also exits in the quarterfinals following a defeat to Czech Tomas Berdych . Serena Williams reaches the semifinals by ousting Cincinnati 's Simona Halep .