Serena Williams goes into last four as Pennetta quits

(Reuters) - Serena Williams enjoyed an easy passage into the semi-finals of the Italian Open tennis on Friday when her opponent Flavia Pennetta retired with a right wrist injury.

The Italian, ranked 21, had treatment at 3-0 down and decided to quit when Williams was leading 4-0 and 40-0.

Williams, who won last week's title in Madrid, will play either China's Li Na or Dominika Cibulkova of Slovakia in the last four.

Holder Maria Sharapova was due to play Venus Williams later on Friday while Wimbledon champion Petra Kvitova was scheduled to face Angelique Kerber of Germany.