The 22-year-old Cibulkova will now appear in her third career major quarterfinal and her first-ever one at the All England Club.
Cibulkova should have her hands full with the three-time Grand Slam champion Sharapova in the round of eight.
Meanwhile, ninth-seeded Marion Bartoli outplayed a seventh-seeded Serena to post a 6-3, 7-6 (8-6) upset on Court 1. The hard-hitting Frenchwoman needed five match points to end Serena's reign.
The former world No. 1 Serena had won her last 17 matches here before running into the determined Bartoli, who lost to Serena's older sister Venus in the 2007 Wimbledon finale.
Bartoli had a relatively easy time of it in the first set Monday before Serena picked up her game in the second.
Serena saved three match points while trailing 5-6 in the second, including a brilliant rally that ended with a overhead smash by the 13-time Grand Slam champ. The American star then held on to break Bartoli in that game to force a tiebreak.
Bartoli would enjoy two more match points in the tiebreak, and converted on the second with an unreturnable serve.
The Frenchwoman advanced in just under two hours, as she out-aced Serena, 10-8, and recorded two service breaks, compared to only one for the American superstar.
The 26-year-old Bartoli will now appear in her second career Wimbledon quarterfinal, where she'll face big-serving German Sabine Lisicki.
"This year I'm in the best shape of my life and I'm playing some great tennis right now," Bartoli said. "Beating Serena is almost like a dream come true. Even though she didn't play for almost one year, she's probably one of the greatest champions in women's tennis."
Serena, of course, finally returned to action two weeks ago after being sidelined by a series of health issues for almost a year after capturing a fourth Wimbledon championship last July. She beat Russian Vera Zvonareva in last year's finale on the famed Centre Court.
"I never came here thinking I would lose," Serena said. "That's my attitude. You win some and you lose some. Today just happened to be the one that slipped under me."
"I think I did really well just being able to come back and play and win some matches, and just really play tough," Serena added. "Even today I lost, but I was able to kind of hang in there and play tough. And I can only get better. That can potentially be really scary, because I can only go up from here and I can just do so much more."
A 23rd-seeded Venus, playing in her 15th Wimbledon, succumbed to Tsvetana Pironkova for a second straight year on the hallowed lawns, as the 32nd seed stunned the former No. 1 star 6-2, 6-3 on Centre Court.
"I didn't seem to get the ball in," Venus said. "She took her opportunities. I just didn't put the ball in the court, simple as that. Unfortunately, I seem not to have my good days against her. But she played well."
Pironkova and Venus played in front of the Duke and Duchess of Cambridge -- Prince William and his new wife Kate -- on Monday.
The 23-year-old Pironkova, who had been suffering through a miserable 2011 campaign, stunned Venus in 1 hour, 15 minutes by breaking the American's big serve four times, compared to only one break for Venus.
"I beat her two times, two consecutive years...it feels amazing to play such a champion on this legendary court," Pironkova said. "When I come here I just feel so relaxed. I really like the atmosphere here."
Pironkova was a dismal 4-14 this season before heading to Wimbledon, where she's now 9-1 over the last two years.
The Bulgarian Pironkova is now 3-1 lifetime against Venus, including an identical 6-2, 6-3 quarterfinal victory here a year ago. She also beat the American in the opening round at the 2006 Australian Open and is 3-0 in their all-time series at the majors.
The seven-time Grand Slam champion Venus is an eight-time Wimbledon finalist, going 5-3 in those title tilts.
Venus, like Serena, returned to action two weeks ago after being sidelined for five months because of hip and abdominal injuries.
This marked the first time that the mighty Williams sisters both lost at Wimbledon on the same day. It will also mark the first time in five years that neither sister will appear in the quarterfinals here.
"Definitely not our best day," Venus said. "I think we both envisioned seeing this day going a little bit different."
"Obviously it's not something planned," Venus added. "We rarely lose on the same day."
Meanwhile, Sharapova, this year's fifth seed and the 2004 winner at the All England Club, breezed to a 6-4, 6-2 win over 20th-seeded Chinese Peng Shuai.
Sharapova did not drop a service game on Monday and committed just 10 unforced errors. The Russian star is back in the Wimbledon quarterfinals for the first time since a semifinal run in 2006. She had been eliminated in the fourth round twice and the second round twice since.
Fourth-seeded Belarusian Victoria Azarenka will return to the quarterfinals for the second time in three years after a 6-2, 6-2 thumping of Russia's Nadia Petrova. She's never been past the quarterfinals of a Grand Slam and this year was eliminated by Li Na in each of the first two major championships -- in the fourth round at the Australian Open and in the quarters at Roland Garros. Li went on to the final in Melbourne and captured the title in Paris, but has already been eliminated in London after falling to Lisicki in the second round.
Up next for Azarenka, the highest seed still standing at this fortnight, will be capable Austrian Tamira Paszek.
Eighth-seeded Petra Kvitova improved to 9-1 in her last 10 matches at the All England Club by clobbering 19th-seeded Belgian Yanina Wickmayer 6-0, 6-2. The Czech lefthander will now appear in her third quarterfinal in her last five Grand Slam events. She also appeared in this year's round of eight at the Aussie Open.
The 21-year-old Kvitova, a three-time titlist on tour this season, will meet Pironkova in the quarters.
Lisicki landed in the Wimbledon quarters for a second time by getting past Czech Petra Cetkovska 7-6 (7-3), 6-1. The German reached the round of eight two years ago, but missed the tournament last year because of an ankle injury and has proven that grass is a surface that suits her game as she captured the Wimbledon tuneup in Birmingham earlier this month.
Paszek landed in her first-ever major quarterfinal with a 6-2, 2-6, 6-3 victory over fellow 20-year-old Ksenia Pervak of Russia.
All four women's quarterfinals will be staged on Tuesday. All eight of the remaining women hail from Europe.