ranked Rafael Nadal struggled past big-serving Ivo Karlovic 5-7, 6-1, 7-6 (7) Thursday to reach the BNP Paribas Open semifinals for the sixth consecutive year. Nadal, who won on his third match point when Karlovic's forehand sailed long, set up a semifinal against Juan Martin del Potro Saturday. The Argentine progressed when his opponent Tommy Robredo of Spain withdrew before the match due to an abductor muscle strain. Nadal led 5-2 in the tiebreaker before Karlovic tied it up with a backhand volley winner. The Croat came up with the same shot to spoil Nadal's first match point. Nadal set up his second match point with a forehand that landed just inside the sideline, but his forehand error allowed Karlovic to tie it 7-all. Nadal's forehand winner in the corner gave him a third match point and he finally converted on Karlovic's error. On the women's side, top-ranked Caroline Wozniacki reached the semifinals when Victoria Azarenka retired with a hip injury while trailing 3-0 in the first set. Wozniacki next plays Maria Sharapova, who outlasted Peng Shuai 6-2, 5-7, 6-3 to reach her first semifinal of the year after missing the last five weeks with a viral illness. Sharapova needed more than two hours to overcome Peng in a match that featured 13 service breaks. They traded breaks in the first four games of the third set. Serving at 3-2, Sharapova won the final four games of the match, clinching it with an inside-out forehand off Peng's second serve. During the Wozniacki and Azarenka match, a Japanese flag was tied to the chair umpire's tower and written on it in black marker were the words, ‘Our thoughts are with you! Caroline and Victoria.' After Azarenka left, Wozniacki untied it and held it up in tribute to the victims of the recent earthquake and tsunami. By reaching the semifinals for her fourth straight tournament, Wozniacki guaranteed she will retain the No. 1 ranking through the upcoming two-week Sony Ericsson Open in Miami. Robredo hurt himself in his straight-sets win over Sam Querrey, and an MRI Wednesday night confirmed the injury, which will keep him out of the Miami tournament. Del Potro has beaten three seeded players, including defending champion Ivan Ljubicic, to get this far. He's in the semis for his fourth straight tournament after injuries derailed him for much of last year.
