She was the last Wimbledon women’s singles champion of the pre-Williams era and had a near 20 year career at elite level yet even Lindsay Davenport admits to astonishment at the older of the sisters’ longevity.

Having battled for a decade to get the better of Steffi Graf at the sport’s greatest tournament, the American finally did so in 1999 and she went on to win the first Grand Slam event of the new Millennium at the Australian Open, but as defending Wimbledon champion she was beaten in the final in straight sets by Venus as she and younger sister Serena, who had ended Davenport’s reign as US Open champion late in 1999, began their domination of the women’s game.

“It is amazing and she is a huge inspiration,” Davenport said of the woman who was the oldest in the first round draw yet has reached a semi-final at a Grand Slam event for the first time in six years.

“There is no question that when you’ve been at the top and you’ve won all these Grand Slam titles, people do like to keep asking, ‘When are you going to quit?’

“The fans want to know. She has been steadfast that she doesn’t want to quit, she’s not going anywhere and that ‘no one is going to push me out of the sport but me when I feel it’s time’.

“To persevere through a lot of early losses in Slams the last few years for a player who won seven and got consistently to quarters, semis and finals, it is tough to accept that, but she still believes.”

The admiration extends to both sisters who are at the veteran stage of their careers, but are on course to meet one another in the final of a Grand Slam event for the ninth time, while they have also gone well in the doubles as they prepare to team up for the USA at the Rio Olympics.

"It goes to show the athleticism Venus and Serena have," she said.

"When they came up, you could see it but what they’re doing is really, really hard. It’s like what Martina Navratilova did.

“In the most complimentary way, they are such freaks because they’re athleticism is so great. They are amazing specimens and to be able to compete at that level at that age is remarkable. It really goes to show their genetics and athleticism.

“You almost forget Serena is nearly 35. It’s a tough sport and it’s hard to get out of bed some mornings and they make it look so seamless. It’s amazing, they’re so inspirational.”

As top seed Serena looks all but certain to reach yet another Wimbledon final and is the strongest of favourites to claim a seventh title, which would match Graf’s haul at Wimbledon and bring her level with the German’s open era record of 22 Grand Slam titles.

Eighth seed Venus has a much tougher match in prospect, however, against Angelique Kerber who is seeded four places higher and shocked Serena at the final of this year’s Australian Open.

Davenport acknowledged that the 28-year-old German has the quality to prevent another all-Williams final.

“She looks confident again,” she said of Kerber, who alone among the semi-finalists has yet to drop a set in the tournament.

“If she gets past those first few rounds, it seems like something always clicks in her game.

“The serve, though, gives me a little bit of question marks on this surface, when she plays players who can put pressure on the return.

“She is going to have to get a little bit more creative and a little bit more willing to take risks on her serve.

“I imagine she’ll have a good gameplan to beat Venus and know that, on this surface, she’s going to have to be a little bit aggressive.”