Top-seeded Simona Halep of Romania advanced to the Internazionali BNL d'Italia semifinals when Yulia Putintseva retired due to a lower back injury on Saturday in Rome.
Halep was ahead 6-2, 2-0 after 48 minutes when the unseeded Putintseva of Kazakhstan could no longer continue.
Halep saved both break points she faced and converted three of her four break chances.
The runner-up in this tournament to Elina Svitolina in both 2017 and 2018, Halep is one win away from her third final in the Italian capital. Up next is No. 9 seed Garbine Muguruza of Spain, who rallied for a 3-6, 6-3, 6-4 win over Victoria Azarenka of Belarus on Saturday.
Muguruza owns a 4-2 lead in the head-to-head series with Halep, but Halep is 2-0 on clay.
"Every time I played well against her, (I was) as much as possible aggressive," Halep said. "If I play my best game and if I feel great physically on court, I have a big chance to win the match."
Muguruza needed two hours and 19 minutes to dispatch Azarenka and reach the final four at the Foro Italico.
"I knew it was going to be a tough match. She's a good player, she's playing good, she's with a lot of confidence," Muguruza said of Azarenka, who lost a three-setter to Naomi Osaka in the U.S. Open final a week ago.
After a back-and-forth start to the deciding set, Muguruza won 10 consecutive points to set up triple match point.
The other semifinal is an all-Czech affair, with No. 2 seed Karolina Pliskova facing No. 12 Marketa Vondrousova.
Vondrousova, 21, delivered an emphatic upset against two-time Rome champion Elina Svitolina of Ukraine, cruising 6-3, 6-0 in one hour and 20 minutes.
"I think I played an amazing match today. I didn't even expect this, but I'm just happy to be through and happy with this win," Vondrousova said. "I didn't do so many errors, and I hit so many great drop shots. I also served really well, and overall, I think I played a great match today."
Vondrousova won 76 percent of her first-service points, struck 25 winners and saved all nine break points she faced to pick up here third career win against a Top 10 opponent. The fourth-seeded Svitolina had 26 unforced errors and only nine winners.
Pliskova, the defending champion, weathered some mid-match struggles to oust No. 11 seed Elise Mertens of Belgium, 6-3, 3-6, 6-0.
Pliskova finished with 34 winners and 24 unforced errors, compared to 22 winners and 30 miscues for Mertens.
--Field Level Media