2018 French Open champion Simona Halep advanced to the semi-finals of the Italian Open when her opponent Yulia Putintseva retired due to a lower back injury while trailing 6-2 2-0.
The top-seeded Romanian will now meet Spain's ninth seed Garbine Muguruza, who survived an early scare against Victoria Azarenka to beat the U.S. Open runner-up 3-6 6-3 6-4.
Halep said: "Every time I played well against her (Muguruza), I was as much as possible aggressive.
"If I play my best game, and if I feel great physically on court, I have a big chance to win the match. But every time is different, because she's playing so hard. You don't really know what to expect. It's tough."
Twice Rome champion and fourth seed Elina Svitolina of Ukraine, who skipped the US Open to prepare for the claycourt swing, was stunned by Czech Marketa Vondrousova 6-3 6-0.
Number 12 seed Vondrousova will play compatriot Karolina Pliskova in the semis after the defending champion survived a mid-match scare to beat Belgium's Elise Mertens 6-3 3-6 6-0.