Washington - World number two Simona Halep retired with heat illness while Milos Raonic's title drought reached 19 months after Friday's loss to Jack Sock in the ATP and WTA Citi Open quarter-finals.
A day after complaining that severe heat left her feeling "a bit dead," French Open runner-up Halep quit her quarter-final match in even more scorching conditions, allowing Russian seventh seed Ekaterina Makarova to advance 2-6, 6-3, 1-0.
"It was just the heat. I felt a little bit sick and I couldn't continue," Halep said. "I had a headache and I felt sick."
Top seed Halep broke Makarova three times to take the first set in 30 minutes, but the Russian battled back to win the second set and broke Halep to open the third.
Trainers took Halep's blood pressure and said it was fine but the Romanian had had enough.
"Today was really hot," Makarova said. "I was feeling a lot of energy when I came there and the sun took so much energy. After the first set I started putting ice to my face because it was burning. The ice was helping. I was feeling like I could go through the heat. I was fighting to keep going."
Halep played the first match each day she played, escaping rain and after-midnight finishes but competing in the most humid and sweltering conditions.
She sought a later start Friday from organizers but was denied.
"I asked for late today, but I couldn't get it," said Halep, who wasn't upset about the situation.
"I love the city and the tournament," Halep said. "I enjoyed it and I hope to come back."
Halep, who captured her 15th career WTA title in May at Madrid, will defend her title next week at Toronto.
"I'm looking forward to going there," she said. "I can't say I'm going to win the title again because it's going to be tough."
Raonic, who won his biggest career crown in 2014 on the same Washington hardcourts, has gone 30 events since last lifting a trophy last year in Brisbane.
Third seed Raonic has lost five consecutive finals, including last year at Wimbledon, but never got that far this week.
US eighth seed Sock won 12 of the last 14 points in the first set and broke the Canadian in the penultimate game of the second to claim the match in 85 minutes.
"I was able to scrap out some balls and stay in some points to finish it off," Sock said. "It has been crazy humid and hot. I've played in the heat of the day and that gives me a lot of confidence heading into the summer."
Sock, ranked 19th, improved to 3-8 lifetime against Raonic, having dropped eight in a row before a victory last year at Shanghai.
Sock will next face the winner of a later match between Indian qualifier Yuki Bhambri, ranked 200th, and South Africa's Kevin Anderson, who ousted Austrian top seed Dominic Thiem.
Next up for Makarova is a Saturday semi-final against the winner of a later match between French fifth seed Oceane Dodin and Germany's Sabine Lisicki.
Also out to end a title drought is Japanese second seed Kei Nishikori, the 2015 Washington champion who later faces US wildcard Tommy Paul.
Ninth-ranked Nishikori hasn't won a title in 18 months and is also in his 30th event since last taking a crown, at Memphis last year, going 0-6 in ATP finals since then.
German 20-year-old Alexander Zverev, ranked a career-best eighth and seeking his fourth title of the year, faces 21-year-old Russian Daniil Medvedev later.
Results on Friday from the fifth day of the ATP and WTA Citi Open (x denotes seeding):
Jack Sock (USA x8) bt Milos Raonic (CAN x3) 7-5, 6-4
Ekaterina Makarova (RUS x7) bt Simona Halep (ROM x1) 2-6, 6-3, 1-0, retired, heat illness