Williams lost 3-6, 6-3, 7-5 to ninth-seeded Belinda Bencic of Switzerland, who saved two match points in the final set to outlast the seven-time Grand Slam champion despite making 40 unforced errors in the match. She will next face the winner between seventh-seeded Petra Kvitova and Kristina Mladenovic in the round of 16.
Halep, the reigning Wimbledon champion, lost 6-2, 6-3 to unseeded Russian Ekaterina Alexandrova, who earned just her second career win against a top-10 opponent. Halep was playing on back-to-back days after defeating Sweden’s Rebecca Peterson on Sunday. The Romanian has been nursing a back injury that forced her to retire at Wuhan last week.
“It was a tough one today. I didn’t recover well after my first match, so it was very tough for me to play, and she played really well,” Halep said. “The injury from Wuhan, it’s getting worse, so I have to go home and take an MRI … take a break and do some treatment.”
Defending champion Caroline Wozniacki hit seven aces as she cruised past American qualifier Lauren Davis 6-1, 6-3 in her opening match of the tournament. The former No. 1 will face another American, Christina McHale, in the second round.
In her first match since winning the U.S. Open, Canada’s Bianca Andreescu ousted Aliaksandra Sasnovitch of Belarus 6-2, 2-6, 6-1.
The fifth-seeded Andreescu broke her opponent six times and saved 12 of 16 break points for her 14th straight victory.
“I’m on a roll right now. Hopefully I can just keep it up because I think it gives me a lot of confidence,” Andreescu said.
She will next play Elise Mertens in a repeat of the U.S. Open quarterfinals.