Danielle Collins added another major upset to her resume with a massive win over Angelique Kerber.
Danielle Collins def. No. 2 Angelique Kerber 6-0, 6-2
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.
Anastasia Pavlyuchenkova def. No. 5 Sloane Stephens 6-7, 6-3, 6-3
Sloane Stephens' best Australian Open in five years has ended with a 6-7 (3), 6-3, 6-3 loss to unseeded Anastasia Pavlyuchenkova in the fourth round that lasted 2+ hours and finished at nearly 2 a.m.
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.
No. 8 Petra Kvitova takes down Amanda Anisimova 6-2, 6-1
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.
No. 15 Ash Barty eliminates No. 30 Maria Sharapova 4-6, 6-1, 6-4
Ashleigh Barty's run at her home Grand Slam continued when she advanced to the quarterfinals with a 4-6, 6-1, 6-4 win over Maria Sharapova at Rod Laver Arena.
Barty opened the deciding set by breaking Sharapova's serve, helped by two of Sharapova's 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 in the preceding match on the same court.
No. 2 Rafael Nadal def. Tomas Berdych 6-0, 6-1, 7-6 (4)
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.
No. 14 Stefanos Tsitsipas def. No. 3 Roger Federer 6-7. 7-6. 7-5, 7-6
Roger Federer's bid for a third consecutive Australian Open title ended in a surprising 6-7 (11), 7-6 (3), 7-5, 7-6 (5) loss to 20-year-old Stefanos Tsitsipas, the first player from Greece to reach a Grand Slam quarterfinal.
The key stat Sunday night: Federer failed to convert any of the 12 break points he earned. Tsitsipas went 1 for 3 in that category, getting his only break in the last game of the third set.
At 37, Federer was the oldest man left in the field. Tsitsipas is the youngest.
This one was a thriller from beginning to end, both in terms of the high quality and entertaining style of play from both men - long expected of Federer; the world is still learning what Tsitsipas can do.
No. 22 Roberto Bautista Agut def. No. 6 Marin Cilic 6-7, 6-3, 6-2, 4-6, 6-4
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.
Frances Tiafoe def. No. 20 Grigor Dimitrov 7-5 7-6 (6), 6-7 (1), 7-5
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.