Former top-ranked players Venus Williams and Simona Halep both lost in the second round of the China Open on Monday.

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 of 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 Alexandrovam, 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."

World No. 3 Elina Svitolina was made to sweat but avenged her loss in Miami this year against China's Wang Yafan, needing two tiebreaks to move into the round of 16 with a straight-sets victory, 7-6 (5), 7-6 (1).

Wang broke her opponent to open up the initial set, fighting her to deuce relying on cross-court forehands to keep Svitolina out of her comfort zone.

It was a strategy that served the Chinese world No. 49 well in the first; she went on to break again and served for the set at 6-5 only to see Svitolina hold her to love and force the tiebreak.

The second set was a very similar story. The two players traded breaks at the outset but Wang fought to deuce and converted to go a break up at 4-1. But Svitolina bounced back, getting another break of her own to again force a tiebreak that she won with ease.

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.

In the men's tournament, second-seeded Alexander Zverev beat Frances Tiafoe 6-3, 6-2, while fourth-seeded Karen Khachanov of Russia defeated Pablo Cuevas 6-2, 7-6 (7).