American Venus Williams lost 5-7, 6-2, 6-3 to Serb title holder Jelena Jankovic in the Italian Open quarter-finals on Friday while her sister Serena pulled out at the same stage of the tournament with a back injury.
Fifth seed Serena said her withdrawal from her match with 18-year-old French qualifier Alize Cornet should not affect her preparations for the French Open, which starts on May 25.
Cornet knocked out last year's finalist Svetlana Kuznetsova on Thursday and her walkover sets up a semi-final with another Russian, sixth seed Anna Chakvetadze, a 6-2, 3-6, 6-1 winner over Bulgarian qualifier Tsvetana Pironkova on Friday.
Neither seventh seed Venus nor Jankovic were able to stamp their authority on the early phases of their quarter-final, but the American took two of the three first-set games that went with serve to get the upper hand.
The Serb fourth seed came back strongly in the second set, wrapping it up with a forehand down the line into the corner on Venus's serve.
The American paid for too many unforced errors in the final set as Jankovic won five consecutive games on the way to clinching the match.
Jankovic next faces either Russia's Maria Sharapova -- who will become world number one next week after Belgian Justine Henin retired from tennis on Wednesday -- and Swiss ninth seed Patty Schnyder who meet in Friday's late game.
Cornet will be playing in her second Tier 1 semi-final against Chakvetadze after losing to eventual winner Serena at the Family Circle Cup in Charleston last month.
"I'm happy, but it's not the same satisfaction as when you win a real match," Cornet told a news conference.
"Chakvetadze is a very good player. She has been in the top 10 for about two years. She can be aggressive but she has good defence too. She's complete. So I will just do my best and try to play my game."
Chakvetadze had an easy time in the first set against the 64th-ranked Pironkova, who stunned Serbian top seed Ana Ivanovic by beating her in the second round on Wednesday.
The Russian lost her concentration in the second set after Pironkova took time out for treatment on an apparent shoulder problem.
She then stormed back in the decider despite several times needing attention herself on the same area of the body.