MELBOURNE, Australia -- Sloane Stephens' best Australian Open in five years ended with a 6-7 (3), 6-3, 6-3 loss to unseeded Anastasia Pavlyuchenkova in the fourth round, which lasted 2½ hours and finished at nearly 2 a.m. on Monday.
The fifth-seeded Stephens was the 2017 US Open champion and 2018 French Open runner-up, but until this year 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 United States.
Collins, 25, stunned three-time major champion Angelique Kerber 6-0, 6-2 in just 56 minutes on Sunday.
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.
It took four match points and 2 hours, 22 minutes before Barty fended off 2008 champion Sharapova, reaching the quarterfinals of a major for the first time. She is the first Australian woman since Jelena Dokic to reach the last eight at the home Grand Slam tournament. No Aussie woman has won it in 41 years.
"It's amazing that it's ... happening in Australia," Barty said, reflecting on her first goal for 2019. "I have given myself the opportunity and the chance to play in front of the best crowd in the world on one of the best courts in the world and in my home Slam. There is absolutely nothing better."
Sharapova won the first set but was struggling with her serve, and finished with 10 double faults in the match. After dropping the second set -- midway through Barty's nine-game winning streak -- Sharapova took an extended break in the locker room and was booed when she came back to court. That's a rarity for the five-time Grand Slam winner in these parts.
A comeback was always in the cards, and Sharapova nearly delivered -- recovering from 4-0 down in the deciding set, forcing Barty to serve it out, and saving three match points when she did. But Barty held her nerve.
Kvitova, 28, wanted no part of another loss to Anisimova, who beat her last year at Indian Wells and was the youngest American since Jennifer Capriati in 1993 to make it this far at Melbourne Park.
It took her 59 minutes to win 6-2, 6-1. Kvitova was the model of consistency that the two other seeded players previously vanquished by Anisimova -- No. 24 Lesia Tsurenko and No. 11 Aryna Sabalenka -- were not.
She's now on a nine-match winning streak -- her four wins here come after a title run in Sydney last week -- and is into the Australian Open quarterfinals for the first time since 2012.
"When I'm counting the years, it's pretty long," Kvitova said. "But, you know, sometimes the waiting time is worth for it. I'm not complaining at all."
Kvitova broke Anisimova's serve five times -- including the opening game -- and never faced a break point. She got 86 percent of her first serves into play, and won all but five of the points when she did.
"I was going out today as if I'd never played her, because I knew she was going to go out and play her best," Anisimova said. "She came out with a really solid game plan against me. That kind of threw me off, because it was different from my other matches."
The Associated Press contributed to this report.