The fifth-seeded Stephens was the 2017 U.S. Open champion and 2018 French Open runner-up, but she hadn't won a match at Melbourne Park since 2014, when she also lost in the fourth round. The American had all sorts of problems on her serve, facing a total of 23 break points and getting broken seven times, including in the last game.
Pavlyuchenkova, a Russian ranked 44th, played aggressively and compiled a 46-28 edge in total winners. In her fifth Grand Slam quarterfinal, she will face another unseeded player, Danielle Collins of the U.S.
Roger Federer is already talking about a return to the French Open in the wake of his stunning fourth-round loss to Stefanos Tsitsipas at Melbourne Park.
Federer hasn't played on the clay of Roland Garros since his quarterfinal loss in 2015. He was injured in 2016 and skipped the clay season in each of the next two years.
Speaking in French at a news conference after his title defense ended, Federer said he felt like he wanted to play on clay.
"I'm at a moment where I think it would be nice to do it," the 37-year-old Federer said. "I can say I have missed it, I did the right thing skipping it last year, the year before as well, and the year before that I was injured. So I felt I wanted to do it again."
Just one of his 20 Grand Slam titles has been on clay — in 2009 when he beat Robin Soderling in the final. He lost the three previous French Open finals to Rafael Nadal.
Federer said he wants to avoid having a long break in the middle of the year before the grass season.
"I feel that it is not really necessary," he said. "So that's how this was decided."
Stefanos Tsitsipas has become the fifth player on Day 7 of the Australian Open to reach a Grand Slam quarterfinal for the first time. Four of those first-timers have progressed at the expense Grand Slam winners.
Tsitsipas stunned two-time defending Australian Open champion Roger Federer in four sets, ending the 37-year-old Swiss star's bid for three straight titles at Melbourne Park and a record seven overall. Tsitsipas is the first player from Greece to go so far at a major.
Roberto Bautista Agut made it 10th time lucky in the fourth round, ending a run of nine defeats at that stage when he beat 2014 U.S. Open winner Marin Cilic in five sets. Cilic was the runner-up here last year to Federer.
Frances Tiafoe celebrated his 21st birthday by making it to his first Grand Slam quarterfinal with a win over No. 20-seeded Grigor Dimitrov, who has been a semifinalist in Australia and Wimbledon.
On the women's side, Ash Barty beat five-time major winner Maria Sharapova to become the first Australian woman in a decade to reach the quarterfinals at the national championship. American Danielle Collins, who had never won a match at a Grand Slam tournament before this one, stunned three-time major champion Angelique Kerber to make it to the last eight.
Two-time defending champion Roger Federer has been upset in the fourth round of the Australian Open by Stefanos Tsitsipas, who becomes the first player from Greece to reach the quarterfinals at a major.
Tsitsipas converted one of his three breakpoint chances in the match and fended off all 12 he faced to beat the 20-time major winner 6-7 (11), 7-6 (3), 7-5, 7-6 (5).
The 37-year-old Federer had a set point in 10th game of the second for a 2-0 lead but Tsitsipas saved it with a service winner.
Federer has won the last two Australian titles and has six overall at Melbourne Park, a record he shares with top-ranked Novak Djokovic and Roy Emerson.
The 20-year-old Tsitsipas says "I'm the happiest person on earth right now." His best previous run at a major ended in a fourth-round exit at Wimbledon last year.
He will next play Roberto Bautista Agut, who beat 2018 runner-up Marin Cilic in five sets to reach the quarterfinals for the first time. Bautista Agut had lost in the fourth round nine times at Slams.
Bob and Mike Bryan have won their third-round doubles match at the Australian Open in their tournament return as a twin team after Bob's hip replacement surgery.
The fourth-seeded Bryans beat Pablo Carreno Busta and Guillermo Garcia-Lopez 6-3, 7-6 (4). They will play either the 11th-seeded team of Rajeev Ram and Joe Salisbury or the fifth-seeded team of Pierre-Hugues Herbert and Nicolas Mahut in the quarterfinals.
The 40-year-old Americans have won a record 16 Grand Slam trophies as a duo, including six at Melbourne Park, and a total of more than 100 tour titles together. They have spent hundreds of weeks ranked No. 1 in doubles, but Bob was forced off the tour in May because of the deterioration of his hip.
The 10th time was the charm for Roberto Bautista Agut. The 30-year-old Spaniard finally made it to a Grand Slam quarterfinal, edging 2018 runner-up Marin Cilic 6-7 (6), 6-3, 6-2, 4-6, 6-4 at the Australian Open. Agut entered the day 0-9 in fourth-round matches at majors.
Bautista Agut broke Marin Cilic's serve in the ninth game of the last set and held on to beat the 2018 runner-up.
The 22nd-seeded Bautista Agut set up match point with a forehand that nicked the side baseline, then clinched it when sixth-seeded Cilic hit a weak backhand that didn't reach the net.
Bautista Agut's win in 3 hours, 58 minutes advanced the Spanish player to a quarterfinal against either six-time champion Roger Federer or 20-year-old Stefanos Tsitsipas.
Moments after Ash Barty's three-set win over Maria Sharapova, chair umpire Alison Hughes had a bit of a fright when the "Spider Cam" camera operated by the tournament's host broadcaster crashed into a sun canopy over her head.
It has since been shut down.
The camera, which hovers above the court on cables and can move vertically or horizontally over the courts, wobbled in the air for several seconds after it hit the canopy before officials lowered it to the ground.
Tournament officials said the camera has been "shut down while the incident is thoroughly investigated."
The statement added: "The official's welfare was our first priority. She was startled by the incident and has been seen by the medical team. She did not require treatment and will continue working at the event as scheduled."
Petra Kvitova's coach has made an apparently sexist comment about the benefits of on-court coaching in tennis.
Former player Jiri Vanek was asked after Kvitova's fourth-round win at the Australian Open for his thoughts regarding on-court coaching being broadened.
"Last year I was thinking about for sure in women's tennis they help them," he said. "In men's tennis they are more stronger, more tougher maybe like on the court."
The WTA allows on-court coaching, but so far it has not been permitted during Grand Slam tournaments.
Vanek coached 2016 U.S. Open finalist Karolina Pliskova before working with Kvitova, who won Wimbledon titles in 2011 and '14.
Kvitova will play Australia's Ash Barty in the quarterfinals here.
Second-seeded Rafael Nadal has swept to his 20th victory in 24 attempts over Tomas Berdych with a 6-0, 6-1, 7-6 (4) win to advance to the Australian Open quarterfinals.
Nadal won the first nine games of the match and when Berdych finally got on the board in the 10th, the Czech player held his left arm up in mock celebration. Berdych came back strongly in the third set and had a set point in the 12th game before Nadal dominated the tiebreaker.
The last time the players met here in 2015 Berdych beat the Spaniard in straight sets to end a 17-match losing streak against Nadal.
It is the 11th time that Nadal has reached the quarterfinals here. He will next play 21-year-old American Frances Tiafoe.
Frances Tiafoe celebrated his 21st birthday in style with a 7-5 7-6 (6), 6-7 (1), 7-5 win over No. 20-seeded Grigor Dimitrov to advance to his first Grand Slam quarterfinal.
Tiafoe, who received treatment on his right forearm at the end of the third set, broke Dimitrov's serve in the 11th game of the fourth then held serve to end the 3-hour, 39-minute match.
In typical style, Tiafoe took off his t-shirt, flexed his right bicep and waved to the crowd. Then he sat in his chair and covered his head with a towel.
It's a big turnaround for the American at the Australian Open. He lost all three singles matches at the exhibition Hopman Cup three weeks ago, then was beaten in the first round at the Sydney International.
At Melbourne Park, he has beaten No. 5 Kevin Anderson and veteran Andeas Seppi.
Tiafoe will next play either second-seeded Rafael Nadal or Tomas Berdych in the last eight.
Three-time major champion Angelique Kerber was stunned 6-0, 6-2 by Danielle Collins of the U.S. in just 56 minutes in the Australian Open's fourth round. Collins had an 0-5 career record in Grand Slam tournaments until this one. But she has now added an upset of No. 2 Kerber to earlier victories over a pair of seeded women, No. 14 Julia Goerges and No. 19 Caroline Garcia.
Collins was the more aggressive player throughout and finished with a resounding 29-6 edge in total winners.
The former University of Virginia player will face 2017 U.S. Open champion Sloane Stephens or Anastasia Pavlyuchenkova next.
Ash Barty beat Maria Sharapova 4-6, 6-1, 6-4 to reach her first Grand Slam quarterfinal and gave Australian its first woman that deep in its major tournament since 2009.
Barty opened the deciding set by breaking Sharapova's serve, helped by two of Sharapova 10 double-faults in the match. It came minutes after the capacity crowd lustily booed Sharapova when she returned from an extraordinary long toilet break after the second set.
Barty broke 2008 champion Sharapova's serve again to lead 3-0, helped by two unforced errors by the Russian and went up 4-0 while holding serve with four straight points. Sharapova faced more break points in the next game but held serve, ending a winning streak of nine consecutive games by Barty.
Sharapova, who beat defending champion Caroline Wozniacki in the third round, broke Barty's serve in the next game and then closed to 4-3 in a game which included the point of the tournament — a 21-shot rally that included great gets by both players and ended with a wide backhand by Barty.
Barty was forced to save two break points in the next game, but held to go up 5-3. After Sharapova held in the next game, she saved one match point before Barty ended the 2-hour 22-minute match with an ace.
The Australian will next play two-time Wimbledon champion Petra Kvitova, who beat 17-year-old American Amanda Anisimova in straight sets.
Two-time Wimbledon champion Petra Kvitova is the first player into the Australian Open quarterfinals after beating 17-year-old American Amanda Anisimova 6-2, 6-1 to open play Sunday at Rod Laver Arena.
Kvitova, who had a WTA Tour-leading five tournament wins last year, extended her winning streak to nine matches after capturing the Sydney International title last week and her four wins at Melbourne Park this week. She hasn't made the quarterfinals here since 2012.
Anisimova, one of three American women playing fourth-round matches Sunday, beat seeded players in the second and third rounds. She was the youngest player to reach the Round of 16 here since 2006 and the youngest in any Grand Slam tournament since 2007.
Two-time Wimbledon champion Petra Kvitova opens play at Rod Laver Arena on Day 7 of the Australian Open with a match against 17-year-old American Amanda Anisimova.
Anisimova has beaten two seeded players on her way to the fourth round and a win Sunday would advance her to a quarterfinal against either Ashleigh Barty or Maria Sharapova, who meet in the following match at Rod Laver.
Rafael Nadal is to play his Round of 16 match against Tomas Berdych. Six-time champion Roger Federer, playing in his 20th Australian Open, takes on 20-year-old Stefanos Tsitsipas to open night play.
The weather is mostly sunny with an expected high temperature of 24 Celsius (75 Fahrenheit).
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