Simona Halep is two victories away from a first Italian Open title after opponent Yulia Putintseva retired injured during their quarter-final clash in Rome.
Halep was leading 6-2 2-0 when her opponent called it a day because of a lower back problem.
Top seed Halep has twice lost in the final at the Foro Italico and is chasing the one major clay title she is yet to claim.
In the last four, Halep will take on another former French Open champion, Garbine Muguruza, who battled to a 3-6 6-3 6-4 victory over Victoria Azarenka.
Azarenka has exceeded expectations after her quick switch to clay following the US Open final last weekend and started strongly but it was Muguruza who emerged victorious.
"It's one of the biggest goals now. I love Rome, I love Italy, and every time I have a chance I come on holiday here, so I feel really good when I play here in Italy," 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."
Two-time Rome champion and Ukranian fourth seed Elina Svitolina, who skipped the U.S. Open to prepare for the claycourt swing, was stunned by Czech Marketa Vondrousova 6-3 6-0.
The Number 12 seed 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.
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