Venus Williams gained revenge on her sister Serena's behalf with a 6-0 6-2 win over Jill Craybas.
By Caroline Cheese
BBC Sport at Wimbledon
Craybas knocked out Serena on Saturday to prevent the sisters meeting in the last 16, but Venus ensured the American did not complete a Williams double.
The twice former champion raced through the first set and recovered from 2-0 down in the second to complete a comprehensive victory.
Williams, seeded 14th, will face France's Mary Pierce in the last eight.
"I think it's a big challenge mentally to play Serena and I in a row," said Venus afterwards.
"So I was lucky to be the second sister, but my game is good. I'm raising things to the next level.
She added: "I definitely would like to win it a little bit for my sister, but mostly for me."
Venus now plays Mary Pierce, who made the last eight with a 6-3 6-1 defeat of Flavia Pennetta.
Pierce's supporters, who packed out Court Three long before the start, gave her full backing as she made the last eight for only the second time in her career - the last in 1996.
She moved ahead in the baseline battle by breaking in a long eighth game.
Pennetta was rattled and could not hit back, and although she defiantly saved four match points, Pierce eased home.
"I feel really good, I definitely feel the difference," she said. "I feel that I'm on the right path and that like I'm actually improving every day.
"Being injured and not able to be physically fit and in shape to play my game was very difficult for me but now I can do that and I am very happy.
"I'm just going to do my usual thing against Venus and see how it goes."