Sarena Williams in semis after Penetta retires

Flavia Pennetta, right, shakes hands with Serena Williams of the US after retiring from their quarterfinal match at the Italian Open tennis tournament, in Rome, Friday.

Sarena Williams advanced to the semi finals at the Italian Openon Friday after Flavia Pennetta retired with a right wrist problem while trailing 4-0 in the first set.The Italian player called for the trainer after falling behind 3-0. She had her wrist re-taped, but conceded during the fifth game after 28 minutes of play.The victory extended Williams' winning streak to 17 matches following titles in Charleston and Madrid. She also has two victories in Fed Cup.Williams will face the winner of match between French Open champion Li Na and fourteenth-seededDominika Cibulkova in the semifinals.Older sister Venus Williams plays defending champion Maria Sharapova later Friday.On men's side, top-ranked Novak Djokovic meets No. 5 Jo-Wilfried Tsonga and five-time champion Rafael Nadal faces Tomas Berdych.Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.