By Chris Bevan
BBC Sport at Wimbledon
Neither Venus or Serena have dropped a set on their way to the last eight
Sisters Venus and Serena Williams both moved ominously into the quarter-finals at Wimbledon after easing through their fourth-round matches on Court Two.
Venus was never close to her best form against Russia's Alisa Kleybanova but always looked firmly in control.
The defending champion let a 5-1 second-set lead slip away but sealed a 6-3 6-4 win on her fifth match-point.
Serena was simply too powerful for her fellow American Bethanie Mattek and swept to a convincing 6-3 6-3 win.
With second seed Jelena Jankovic losing to Thailand's Tamarine Tanasugarn and fourth seed Svetlana Kuznetsova crashing out to Poland's Agnieszka Radwanska, the Williams's will be eyeing their first final against each other since 2003.
Venus will now take on the unseeded Tanasugarn while Serena faces 14th seed Radwanska in the quarter-finals.
Between them, the sisters have won six of the last eight Wimbledon women's titles, with Serena's successes both coming against Venus in the finals of 2002 and 2003.
Their big-hitting game is undoubtedly best suited to grass and has allowed them to each win their four matches here so far this year without dropping a set.
Four-time champion Venus, 28, has done so despite looking prone to errors and her win against Kleybanova was achieved in similar style.
She was clearly unhappy at being asked to play out on Court Two, known as the 'Graveyard of Champions', rather than on one of the Show Courts.
"There is not too much I am going to say about that in the press," Venus said. "Obviously we know wherever we play we have to play well and that is pretty much all I'm going to say about that."
Venus agreed that men's champion Roger Federer would not be moved around the courts in similar fashion, saying: "You said it. It is true."
Like her sister, Venus had lost on this court before, and she admitted conditions there were tricky.
"I've played a lot of matches there before and it does play differently," she explained. "And I felt a little cramped. I like to have room to move and there is less on either side of the court.
"But I had to focus and take those factors into account."
Serena also found it unlikely that Federer would be asked to play on Court Two.
"I have not seen Roger Federer on Court Two for six years, so I could not imagine it," Serena said.
"Initially, when I saw the schedule I thought it was a mistake.
"It wasn't what I wanted but I couldn't dwell on it. I had to focus on winning my match and it gave me extra motivation to get through it.
"I haven't been given an explanation why it happened but I do think it is weird to have a defending champion who has won this tournament four times on Court Two. I have only won it twice.
"It is a question best asked to the All England Club, who would be able to address it better."
Venus took time to get to grips with the Russian Kleybanova's serve but once she put her under pressure, she quickly broke to take a 5-3 lead.
But the seventh seed was not exactly dominant on her own delivery and relied more on Kleybanova's mistakes as she served out for the set.
The number of loose shots being played by the world number 42 increased at the start of the second set and a clean forehand winner down the line saw her move a break up.
You have to be ready. No match is a given - you have to go out there and work for it
Kleybanova continued to unravel and Venus looked on the brink of victory at 4-1 before she herself wobbled.
Venus had to save two break points at 15-40 before taking that game thanks to a contentious line call that left Kleybanova stunned.
But, to her credit, Kleybanova's challenge did not crumple there and instead she held serve, then fought to save three match points before breaking Venus.
Kleybanova held again to force the champion to serve out for the match at 5-4, forcing three more break points before Venus finally sealed victory with a backhand volley on her fifth match point.
Venus was pleased to make progress and said she was not surprised that so many of the top women's players have already been knocked out.
"The reality is that every player is ready to play," she said. "Everyone comes out with double vengeance and you have to be ready. No match is a given - you have to go out there and work for it."
Serena, 26, had a far easier time of things against Mattek, who had never been beyond the second round of a Grand Slam before this tournament and could not live with the power and pace of the sixth-seed's groundstrokes.
But although she showed more consistency than her sister, Selena was never in spectacular form.
She broke Mattek in the very first game and made the most of several mistakes by the world number 69 to break again and close out the first set in just 29 minutes.
A clever drop shot by Serena and a wild backhand saw Mattek drop serve in her first service game of the second set too and, despite her best efforts, she could not find a way back into the match.