(CNN) -- Twice defending champion Venus Williams moved closer to a Wimbledon title hat-trick on Monday when fourth-round rival Ana Ivanovic left in tears after quitting their Court One match through injury.
Ivanovic concedes to holder Venus in tearful fashion after suffering injury anguish at Wimbledon
Serbia's former world number one lost the first set 6-1 against third-seeded American rival Williams and was serving in the first game of the second when she was forced to stop because of a thigh problem.
Thirteenth-seed Ivanovic returned to court after treatment to win the game, but then quit the match -- handing Williams a place in the last eight in a highly-emotional moment.
"It's very disappointing, especially because I felt my form was getting better and better. It's really frustrating," Ivanovic told media while still struggling to regain her composure.
"The most disappointing thing is I felt like I wasn't given a fair chance to fight. All of a sudden I felt pain after a serve. I didn't feel anything up until that point.
"Over past few days I have felt muscle tightness, but that was normal after playing so much on the grass.
"I was serving at 30-40 down and when I landed I just felt a sharp pain on my inner thigh and I couldn't step on my leg ever since."
Williams now faces Poland's Agnieszka Radwanska, the 11th seed, as she bids to become the first woman to lift three successive Wimbledon singles' titles since Steffi Graf from 1991 to 1993.
Sister Serena, the second seed and a two-time Wimbledon champion, joined Venus in the last eight with a 6-3 6-1 victory over Slovakia's Daniela Hantuchova.
Williams turned up the heat in the first set when her family belatedly took their seats having been on Court One watching Venus. Serena opened a 4-0 lead in the second and took the match in just under an hour.
She now meets eight-seeded Belarusian Victoria Azarenka who battled to beat 10th-seeded Russian Nadia Petrova 7-6 2-6 6-3.
Five-time Wimbledon champion Venus has yet to drop a set in this year's event and has extended her winning streak at the All England Club to 18 matches.
Radwanska, a quarterfinalist last year, triumphed 6-4 7-5 against American teenager Melanie Oudin who had to qualify for the main draw.
Elena Dementieva, semifinalist a year ago, hardly broke sweat as temperatures soared, the fourth seed defeating fellow Russian blonde Elena Vesnina 6-1 6-3 in 70 minutes on Court 2.
Dementieva, making her 11th Wimbledon appearance, never looked back after wrapping up the first set inside 29 minutes and now encounters either France's Virginie Razzano or Italy's Francesca Schiavone for a place in the semifinals.
World number one Dinara Safina, who has yet to win a Grand Slam title, faced 2006 champion Amelie Mauresmo on Centre Court -- and Wimbledon's new roof was shut for the first time during their match when rain fell midway through the second set.
Russian Safina of Russia was trailing at the time having lost the first set. But the top seed recovered for a 4-6 6-3 6-4 win and a last-eight meeting with Sabine Lisicki.
Nineteen-year-old German Lisicki gained a 6-4 6-4 win over world number nine Caroline Wozniacki, of Denmark.