The expectation had been that the pair would meet in the quarter-finals on Tuesday but, while Williams eased to a 6-2 6-2 victory over Carla Suarez Navarro, Barty was beaten 3-6 6-2 6-3 by unseeded American Alison Riske.

Barty had won 15 matches in a row dating back to the Italian Open in May, including her maiden grand slam singles title at the French Open and success on grass at Birmingham that elevated her to the top of the rankings.

But she found grass-court specialist Riske too big an obstacle, with the 55th ranked American recovering from a set down to reach her first slam quarter-final on Monday.

"I'm so incredibly excited," Riske said.

"The fact that it's at Wimbledon, my favourite grand slam, the place that I had always dreamed to be in the last eight club of - they can't kick me out now, I'm here to stay. I am just over the moon."

A dejected Barty was determined to stay focused on the bigger picture.

"It's disappointing right now. Give me an hour or so, we'll be all good," she said.

"The sun's still going to come up tomorrow. It's been an incredible few months. I'm very proud of what we've been able to achieve."

Williams had barely played since the Australian Open because of a knee problem but she is increasingly looking like a clear title favourite.

"The rust is definitely wearing off. Most of all I feel confident that I can actually move and I don't have to go for winners so soon because I'm in pain," the 37-year-old said.

Simona Halep ended the phenomenal run of 15-year-old Cori Gauff with a 6-3 6-3 victory on Court One.

Gauff will now focus on finishing high school.

"These past two weeks have been amazing. I'm excited to be back next year," she said.

Seventh seed Halep is the highest-ranked player left in the women's tournament after Karolina Pliskova and Petra Kvitova joined Barty in tumbling out.

Barty's defeat meant Pliskova could have overtaken her as world No.1 by reaching the final but instead the third seed was beaten 4-6 7-5 13-11 by fellow Czech Karolina Muchova.

Sixth seed Kvitova had been a major doubt for the tournament because of a forearm injury but had won her first three matches in straight sets.

She won the opener against home favourite Johanna Konta, but the British player hit back to win 4-6 6-2 6-4 and will play another Czech, Barbora Strycova, in the last eight.

Strycova staged a tremendous recovery from a set and 5-2 down to beat Elise Mertens while Muchova will face eighth seed Elina Svitolina, who defeated Petra Martic 6-4 6-2.

Halep will face China's Zhang Shuai, who beat Dayana Yastremska 6-4 1-6 6-2.