Holder Maria Sharapova ended the encouraging run of Venus Williams to reach the semi-finals of the Italian Open on Friday, but Serena Williams enjoyed an easy passage through to the last four.
World number two Sharapova downed Venus 6-4, 6-3 in a high-quality encounter to set up a clash with Germany's Angelique Kerber who upset Wimbledon champion Petra Kvitova 7-6, 1-6, 6-1.
Serena was leading Flavia Pennetta 4-0, 40-0 when the Italian retired with a right wrist injury. She will play China's Li Na who beat Dominika Cibulkova of Slovakia 6-1, 7-6.
A break of serve at 4-4 in the first set proved to be the key for Sharapova as she served out and then moved ahead early in the second against Venus.
The American got the break back but immediately handed Sharapova the advantage once more and this time the second seed held on to reach her fifth semi-final of the year.
""I lost to Kerber in Paris in February," Sharapova told a news conference. ""So I'd like to get my revenge in the semi- final.
""I am certainly going to be motivated for that match and hopefully I can play my best."
Venus will be reassured by a rise in her ranking that should be enough to earn her a spot in the United States team for the London Olympics.
The American only returned to the tour in March after six months out with Sjogren's syndrome which saps energy.
For Serena, the extra time off was a relief after a hectic schedule during which she has won titles on clay in Charleston and Madrid.
""It's never nice to go through like that but it is nice to have kind of a semi-day off," Serena said.
""I've been playing every day for I don't know how many days so it definitely helps."
Serena had almost a year off because of a blood clot in one of her lungs, returning to the tour just before Wimbledon.
The world number six said she was now feeling more confident than last summer when she won back-to-back tournaments before losing in the final at the US Open.
""I definitely feel better because I've played more tournaments," she said. ""Last summer my lungs had not recovered completely."
Serena said she expected a tough match against Li who she has never played on clay.
""Li's the defending French Open champion and a great all-court player so it's going to be a really good test for me."
Li let slip a 5-2 lead in the second set before beating Cibulkova, taking the second-set tiebreak 7-4.
Kvitova went into the match with Kerber carrying a stomach injury she suffered earlier in the tournament and the German took advantage to reach the last four.
