ROME -- Danielle Collins has been nearly unbeatable lately. Even with her announced retirement looming.
The 15th-ranked American beat former No. 1 Victoria Azarenka 6-4, 6-3 on Wednesday to reach the Italian Open semifinals and extend her record to 19-1 since early March.
Having won back-to-back titles in Miami and Charleston, South Carolina, recently, she hasn't dropped a set on Rome's red clay.
Collins underwent surgery in 2021 to treat endometriosis and has said she wants to have a child -- which is why she plans to retire at the end of the year.
"A lot of it has to do with my health," Collins said. "Everybody has different ways of ending their professional journey. I want to go out playing my best tennis."
Collins frustrated Azarenka with her aggressive baseline play and even took out her aggression on a TV cameraman at one point, telling him after being approached on a changeover, "Hey dude, you're going to have to back up a little bit."
Late in the second set, Azarenka slammed her racket on the Campo Centrale as her unforced errors piled up. Then Collins slammed her racket, too, after wasting a series of break points. But Collins came up with some clutch serving to finish Azarenka off -- finishing with six aces to Azarenka's none.
"I feel dialed in with my shots and I've gotten better at hitting those small parts of the court," Collins said.
Collins' semifinal opponent will be Aryna Sabalenka, who showed no ill-effects from her previous marathon match as she eased past Jelena Ostapenko, the 2017 French Open champion, 6-2, 6-4.
Sabalenka's win over Collins in the fourth round of the the Madrid Open marked the American's only loss since a defeat to top-ranked Iga Swiatek at Indian Wells on March 8.
All three top-ranked women have reached the final four in Rome as the other semifinal pits Swiatek against No. 3 Coco Gauff.
In men's action, 29th-seeded Alejandro Tabilo of Chile extended his surprising run by beating Zhang Zhizhen 6-3, 6-4 to follow up his upset victories over Novak Djokovic and Karen Khachanov in the previous two rounds.
Tabilo, who hasn't dropped a set during his first appearance in Rome, served an ace down the T on his first match point.
In his first Masters series semifinal, Tabilo will face 2017 champion Alexander Zverev, who beat 11th-seeded Taylor Fritz 6-4, 6-3.
Zverev lost his footing on a service return early in the match, fell to the clay and bloodied his hands and arms. It appeared his left hand got the worst of it but after receiving medical attention he continued playing. He won the point when he got injured.
"My finger is crooked. ... It's starting to be a bit blue," Zverev said of his left pinkie, adding that he wasn't sure if it was broken or not. "I felt pain, but, probably not to the extent that we'll feel it tomorrow."
Zverev plays right-handed but uses a two-handed backhand.
The other quarterfinal matches are scheduled for Thursday. Stefanos Tsitsipas faces Nicolas Jarry -- another Chilean -- and Hubert Hurkacz plays Tommy Paul.
Collins, who reached the Australian Open final in 2022, said she's playing the best tennis of her career.
"It's been nice to have a stretch where I've really been kind of climbing, because, it's not always like that," Collins said. "You have to be really happy for yourself in these moments because it doesn't always work out that way."
Sabalenka, who didn't allow the ninth-seeded Ostapenko a break opportunity, showed no sign of the back problem that required treatment during Monday's three-setter against Elina Svitolina that ended well after midnight local time.
The 26-year-old Sabalenka said she didn't even practice on Tuesday and focused instead on treatment and recovery. And that clearly paid off.
"I would definitely say that it was the best performance of the tournament," Sabalenka said. "I'm super happy that I was able to play without pain today and hopefully with every day I will feel better and better, and I will recover as good as I can for the next match."
Rome is the last big warmup tournament on clay before the French Open starts in 11 days.