American Jessica Pegula reached the semifinals at the Miami Open in abridged fashion when Paula Badosa retired from their quarterfinal match with a viral illness.

Pegula was leading 4-1 after 18 minutes of play when Badosa retired, having won four straight games after dropping serve to start the match.

"I think from her last match I could tell that she probably wasn't going to be 100% by today," Pegula said after the match. "I have no idea what happened or how she was feeling or if she recovered or if it was quick. It's just hard to know in those situations. It can be kind of awkward.

"I didn't really notice that much. I was trying to focus on my side. She broke me first game, and she hit a winner. She's, like, 'Come on.' I was, like, 'Okay, this isn't going to just be another match.'

"But I just tried to refocus on myself, and I don't think I really thought she was going to retire, like maybe not that quickly, maybe a set or, if anything, but not that soon.

"Sometimes you just never know how someone is going to react when they get out there, even though you know they are not feeling well."

Badosa previously took a medical timeout early in the first set of her fourth round victory over 16-year-old Linda Fruhvirtova on Monday, revealing she woke up that morning not feeling well.

Pegula has now won her past two matches in Miami via retirement; she advanced past Anhelina Kalinina in Round 4 after winning the first set 6-0. 

Since the start of last season, Pegula is tied with Badosa and Aryna Sabalenka with a tour-leading five WTA 1000 quarterfinals, but her first semifinal appearance at this level came last summer in Montreal. There, she was beaten by eventual champion Camila Giorgi.

Again bidding for her first WTA 1000 final, Pegula will next faces No.2 seed Iga Swiatek, who took out No.28 Petra Kvitova in straight sets.

"I've definitely played really, really clean tennis the last two sets. Again, I have lost one game in those almost two sets. So [I'm] definitely playing really clean tennis I think right from the start," Pegula said.

"I made semis in Montreal, which was totally different than this tournament, because I think every match I had was three sets. So now this tournament is different scenario.

"No, I think I'm playing really well this week. I think I found my game a little bit. I wasn't feeling too great honestly the whole year, and even in Indian Wells I didn't feel that great.

"But I was able to have a really good practice week the week before the tournament, being here, being home, and kind of found my game again. I'm happy with that."