Serena Williams may never get a better chance of equalling Margaret Court's Grand Slam title record of 24 with the Wimbledon quarter-finals bereft of the leading lights in women's tennis.

The 37-year-old seven-time champion is moving into something resembling her best form after an unconvincing first week but will not take Tuesday's quarter-final opponent Alison Riske lightly.

That would be wise after the 29-year-old American ousted world number one Ashleigh Barty in the last 16.

Barty was then followed out of the tournament by third seed Karolina Pliskova, two-time champion Petra Kvitova and 15-year-old Coco Gauff.

Riske was looking forward to facing her American compatriot when she said: "Bring it on!" Williams knows Riske relatively well -- they have played doubles together -- and is aware on the grass she can hold her own as well as the fact the last time she faced a relatively unheralded American, Sofia Kenin at the French Open, she lost.

"She's (Riske) a fighter on the court," said Williams.

"She's playing really great, especially on the grass. She's attacking that ball really well. She doesn't let anything limit her."

Williams is ominously talking up her improvement as the tournament has gone on after a knee problem affected her clay court campaign.

"The rust is definitely wearing off," she said.

"Most of all I feel confident that I can actually move and I don't have to, like, go for winners so soon because I'm in pain.

"It's like, Oh, now I can just play my game, hit shots, not have to worry about anything else.

"It's good when your mind is clear and you can just play."

 - 'Life is so nice to me' -

For Riske, reaching a first Wimbledon quarter-final is an early wedding gift ahead of her marriage which takes place just after the tournament.

"I'm ready for a war (with Williams). She's the greatest athlete I think that's ever been on the women's side," she said.

Waiting for Williams or Riske could well be Britain's French Open semi-finalist Johanna Konta, who must beat Czech veteran Barbora Strycova to reach her second Wimbledon semi-final.

Strycova, who beat Konta in their only previous meeting, had been talking of retirement prior to her 17th Wimbledon campaign.

The rest of the quarter-finals have just two seeds involved -- number seven Simona Halep and eighth seeded Elina Svitolina.

Former world number one Halep -- who has never been beyond the quarter-finals at Wimbledon -- plays China's Zhang Shuai, who was close to retirement in 2015, while Svitolina takes on Pliskova's conqueror Karolina Muchova of the Czech Republic.

Zhang's change of mind over retiring was down to advise from her doubles partner and close friend Australian Sam Stosur.

"That got me to thinking maybe, okay, I'm going to the Australian Open one more time, one more try," she recalled of the chat with Stosur.

"I'm really, really happy I tried one more time, and also we won this year in the Australian Open doubles.

"So life is so nice to me."

Of all the players to go out on Monday, Barty's is undoubtedly the biggest boon for Williams.

Having looked so assured in the first week -- and a decent bet to end nearly four decades of Australian being without a women's singles champion -- she lacked the answers when required as Riske fought back to win 3-6, 6-2, 6-2.

There was one consolation for Barty as Pliskova could have taken her number one spot but the Czech third seed went out as well in a marathon duel, beaten by Muchova 4-6, 7-5, 13-11.

"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.

Muchova meanwhile can call upon star power of Hollywood Rebel Wilson, the actress from Bridesmaids and the Pitch Perfect series of movies.

"It's crazy. She texted me last year when I beat Muguruza (at the US Open). I was, like, Wow. I was surprised about that.

"Yeah, she's just super chill and super nice person."