Barty exits Wimbledon as Serena coasts through

London - World number one Ashleigh Barty's hopes of becoming the first Australian women's champion in nearly four decades were dashed on Monday opening the way for Serena Williams to potentially equal the all-time Grand Slam haul.

Having looked assured last week, while Williams was not altogether convincing, it was the 23-year-old Australian who cracked and went down in three sets to unseeded American Alison Riske 3-6, 6-2, 6-2.

Barty's defeat also leaves 15-year-old Coco Gauff as a significant title contender.

Gauff, who needs to reach the semi-finals to emulate the then 15-year-old Jennifer Capriati's run in 1991, is playing former world number one Simona Halep. 

Williams, bidding for a 24th Grand Slam title to tie with Australian Margaret Court, will play Riske next after trouncing Carla Suzarez Navarro 6-2, 6-2.

"It is a tough one to swallow but I lost to a better player," said Barty, who had been hoping to become the first Australian champion since Evonne Goolagong Cawley won her second title in 1980.

For Riske it was perhaps an unexpected early wedding present -- she gets married after Wimbledon Stephen Amritraj, the son of former Indian Davis Cup player Anand -- but extremely well-earned.

It will be the 29-year-old's first appearance in a Grand Slam quarter-final.

"I had to play aggressive. I had to take it to Ash," said Riske

"The grass definitely brings out the best in me. Hopefully it will rub off and happen in other places too."

The prospect of palying 37-year-old Williams did not have her knees knocking together in fear either:  "Bring it on!"

Williams, whose clay court season was affected by a knee injury, said the hunger for the game and for victory is as strong as ever. 

"I always get excited," said Williams after her victory which put her into a 14th Wimbledon quarter-final.

"I'm a really pumped player. That's my personality. Of course I still I want it or else I wouldn't be here."

Williams has teamed up with another former world number one Andy Murray in the mixed doubles to accrue more matches and she said that the more she played she more she was finding her rhythm. 

"I definitely had more matches this week than the past five months, so yikes!" said Williams.

"It definitely is good, I know that I can play and now that I'm feeling better physically, I almost feel a relief more than anything.

"Finally I can play tennis."

Williams, who won her first match with Murray on Saturday, said she will not be taking Riske for granted.

"Last time I faced a fellow American, I lost," she said in reference to her loss to Sofia Kenin at Roland Garros

"She's great on the grass and took out the number one player in the world who's just won a grass court tournament (Barty won in Birmingham)."

Zhang Shuai became the first Chinese woman since Li Na in 2013 to reach the Wimbledon quarter-finals.

World number 50 Zhang defeated Ukraine teenager Dayana Yastremska 6-4, 1-6, 6-2.

The 30-year-old will face either Gauff or Halep for a place in the semi-finals.

Wimbledon results on Monday (x denotes seeding):

Men

4th round

Roberto Bautista Agut (ESP x23) bt Benoit Paire (FRA x28) 6-3, 7-5, 6-2

Rafael Nadal (ESP x3) bt Joao Sousa (POR) 6-2, 6-2, 6-2

Women

4th round

Alison Riske (USA) bt Ashleigh Barty (AUS x1) 3-6, 6-2, 6-3

Serena Williams (USA x11) bt Carla Suarez Navarro (ESP x30) 6-2, 6-2

Barbora Strycova (CZE) bt Elise Mertens (BEL x21) 4-6, 7-5, 6-2

Elina Svitolina (UKR x8) bt Petra Martic (CRO x24) 6-4, 6-2

Simona Halep (ROU x7) bt Cori Gauff (USA) 6-3, 6-3

Zhang Shuai (CHN) bt Dayana Yastremska (UKR) 6-4, 1-6, 6-2