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Danielle Collins had never won a Grand Slam match prior to this year's Australian Open

Australian Open 2019 Venue: Melbourne Park Dates: 14-27 January Coverage: Daily live commentaries on the BBC Sport website, listen to Tennis Breakfast daily from 07:00 GMT on BBC Radio 5 live sports extra and watch highlights on BBC TV and online.

Wimbledon champion Angelique Kerber and fifth seed Sloane Stephens were both knocked out of the Australian Open in the fourth round.

American world number 35 Danielle Collins thrashed second seed Kerber 6-0 6-2 in 56 minutes.

Collins, 25, will face Anastasia Pavlyuchenkova in the quarter-finals after the Russian beat 2017 US Open winner Stephens in a marathon match.

Pavlyuchenkova, the world number 44, won 6-7 (3-7) 6-3 6-3.

The first game of the deciding set was a 17-minute battle that went to deuce 10 times as Stephens fended off eight break points.

"I really appreciated that some of you guys stayed," said Pavlyuchenkova after the match finished at 01:53 local time.

"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."

Collins, who is making her Australian Open debut at the age of 25, had lost in the first round of her five previous Grand Slam appearances.

"I may not have won a Grand Slam match before coming here but, I've got to tell you, I think it's going to keep happening," she said.

"I just go out fearless, and give it my all."

Opportunity goes begging for Kerber

Angelique Kerber reached the semi-finals of the Australian Open last year

World number two Kerber was among the favourites for the title and had dropped just 10 games in the previous three rounds.

"I was feeling good but you have sometimes days like this," said the three-time Grand Slam champion. "I was trying but couldn't find my rhythm."

"I wasn't able to play my tennis, my solid game. I wasn't moving good. My serve wasn't as good as it has been in the last few days."

Collins, who is relatively unknown on the WTA Tour after playing much of her tennis in the US collegiate system, was a resounding underdog but breezed through the opening set in 20 minutes.

The American hit 29 winners in the match and broke six times in total - winning almost 70% of the overall points.

Kerber looked to begin a comeback at the start of the second but was immediately pegged back before Collins smashed a backhand to break the German's serve again and take a 4-2 lead.

Collins needed just one match point to break again at the end and claim a ruthless victory.