World number two Angelique Kerber was ousted the Australian Open by unseeded American Danielle Collins on Sunday in the biggest upset yet in the women’s draw at this year’s season-opening Grand Slam.

The day ended with another upset as unseeded Russian Anastasia Pavlyuchenkova ground down American fifth seed Sloane Stephens in a late-night epic that ended in the early hours of Monday, local time.

The world number 44 beat Stephens 6-7 (3/7), 6-3, 6-3 to set up a last eight clash with another American, Danielle Collins who knocked second seed Angelique Kerber.

“I really appreciated that some of you guys stayed,” said the Russian, who also make the quarter-finals in 2017.

“I heard someone was yawning during the match though, so I’m sorry. I thought it was quite an exciting match, but anyway I’m happy I stayed awake.”

Former US Open champion Stephens took an early break in a match that began at 11:23 pm Sunday due to yet another scheduling logjam at the season-opening Grand Slam.

But she blew a 4-1 first set lead as Pavlyuchenkova broke back and forced a tie-break, which the American won 7-3 to take the first set after 61 minutes.

She gained an edge again to open the second, only to give away a double break, allowing the Russian to serve it out after 43 minutes.

The first game of the decider was a 17-minute arm wrestle that went to deuce 10 times as Stephens fended off eight break points, prompting cries of “hurry up” from the few remaining spectators.

Stephens’ mistake rate climbed as the match wore on and Pavlyuchenkova finally secured the win at 1:53 am.

This year’s tournament featured the latest ever women’s match when Spain’s Garbine Muguruza defeated Briton Johanna Konta in a second-round clash that began at 12:30 and ended at 3:12 am.

Konta later slammed the scheduling as “dangerous” and unhealthy.

Big win for Collins

Collins, making her debut in the tournament main draw, humiliated the German three-time major champion 6-0, 6-2 to set up a quarter-final clash with either fifth seeded fellow American Sloane Stephens or Russia’s Anastasia Pavlyuchenkova.

Ranked 35 in the world, she is little known on the WTA Tour after playing much of her tennis in the US college system.

Before this year’s tournament she had never won a match at a Grand Slam in five attempts and Kerber trounced her 6-1, 6-1 in their only previous meeting last year.

The delighted American, who also eliminated two seeds in the opening rounds, said she was developing a taste for success at the Majors.

“I may not have won a Grand Slam match before this, but I gotta tell you, I think it’s going to keep happening,” she said. “I hope to have many more of these.”

Hometown hero Ashleigh Barty muscled past Maria Sharapova to reach her first Hrand Slam quarter-finals where she will meet Petra Kvitova who matched her best Slam performance since a terrifying knife attack derailed her career.

On a hot day on Rod Laver Arena, the in-form 15th seeded Australian brought the Russian’s drive to win a first Grand Slam since the 2014 French Open to a grinding halt 4-6, 6-1, 6-4.

Five-time major winner Sharapova claimed her biggest scalp since completing a drugs ban in 2017 when she rolled defending champion Caroline Wozniacki in round three and looked on track to carry the momentum forward.

The 30th seed won the first set but then fell to pieces in front of a parochial crowd who booed her at times, losing nine games in a row to surrender the second and go two breaks down in the third.

Despite offering some late resistance, and some unbelievable tennis, there was no way back for the 2008 champion.

“She is an absolute champion,” Barty said of Sharapova. “She was never going to go away. I knew I had to keep chipping away – in a sense, trust the work we’ve done. I know that I can match it with the best.”

The diminutive Barty, 22, has been in sizzling form, winning seven of eight matches this year to back up a title victory in Zhuhai late last year.

Her win makes her only the third home player this millennium to reach the last eight in Melbourne, following Alicia Molik in 2005 and Jelena Dokic in 2009.

Kvitova schools teen sensation Anisimova

Next up is Kvitova, who beat Barty in the final of the warm-up Sydney International this month.

The two-time Wimbledon champion blazed her way into the quarter-finals with an emphatic straight sets win over 17-year-old Amanda Anisimova.

The Czech eighth seed downed the unseeded American 6-2, 6-1 to match her best performance at a major since being slashed in a terrifying attack at her home in late 2016 that left her with lasting nerve damage in her fingers.

She gingerly returned to action at the 2017 French Open and made the quarters at Flushing Meadow that year, with her efforts Sunday the best since then.

“I’m feeling good. It is important for me to enjoy time on the court and playing tennis, which is the main thing for me,” said the Czech, who is in the quarters at Melbourne for the first time since 2012.

“And being in the quarter-final and in the second week of a Grand Slam, I’m really enjoying it.”

Women’s singles - 4th round

Petra Kvitova (CZE x8) bt Amanda Anisimova (USA) 6-2, 6-1

Ashleigh Barty (AUS x15) bt Maria Sharapova (RUS x30) 4-6, 6-1, 6-4

Danielle Collins (USA) bt Angelique Kerber (GER x2) 6-0, 6-2

Anastasia Pavlyuchenkova (RUS) bt Sloane Stephens (USA x5) 6-7 (3/7), 6-3, 6-3

With inputs from AFP