PHOTOS: Big upsets on Day 4 at Australian Open

From potential dark horses to former champions, here are the players who were knocked out of  the Australian Open on Thursday

Wawrinka sent out by Sandgren

Hobbling former champion Stan Wawrinka was knocked out of the Australian Open by American Tennys Sandgren on Thursday, losing 6-2, 6-1, 6-3 on the Margaret Court Arena.

The Swiss 32-year-old looked to be struggling with his movement against the world number 97, clutching his knee throughout the match, especially when forced wide.

Sandgren, 26, played rock-solid tennis to claim only his second grand slam singles victory having opened his account against Frenchman Jeremy Chardy in the first round.

He completed victory with an ace.

Wawrinka had right knee surgery in August and Tuesday's victory over Ricardas Berankis was his first match for six months, having only declared himself fit last weekend.

Muguruza outplayed by Su-wei 

Garbine Muguruza will not forget her first career encounter with Hsieh Su-wei in a hurry.

Spanish third seed and many people's Australian Open favourite blazed away in searing heat trying to solve the puzzle set by the 32-year-old, who previously had managed only two wins against players ranked in the top 20 in 17 years on Tour.

The trouble was that her main weapon, the sledgehammer groundstrokes, proved futile as she slumped to a 7-6(1) 6-4 defeat to Hsieh.

Muguruza, who needed treatment early on for a blister on her foot, found her heaviest hits coming back in unusual places and to make matters worse she was often left flat-footed by her Taiwanese opponent's punchy and flat double-handed groundstrokes, apparently manufactured with minimum effort.

The 24-year-old chalked up 43 unforced errors during the match. Her frustration could have cost her a default when she swiped a ball dangerously close to a line judge when serving at 5-6 in the opening set.

Instead she received only a warning from the match umpire.

Muguruza refused to blame the heat, which soared to 39 degrees Celsius, the blister, or a strapped right thigh for her earliest loss in Melbourne since a second-round thrashing by Serena Williams five years ago.

"She's definitely a very tricky opponent," she said.

"I think today she played well. I maybe could have done things better, but at the end, she deserves to win. That's really it."

Konta ousted by lucky loser

Lucky loser Bernarda Pera sent ninth seed Johanna Konta tumbling out of the second round of the Australian Open on Thursday with a 6-4, 7-5 upset in blazing sunshine on court two.

A lacklustre serving display from the British number one - she failed to land a single ace - allowed lefthander Pera ample opportunity to showcase her powerful returns off both sides and the 23-year-old American duly delivered.

A single break of serve for 5-4 was enough for the world number 123 to sew up the first set after 39 minutes when Konta sent a backhand long, and Pera was soon all over the Briton's serve in the second.

Konta, a semi-finalist at MelbournePark in 2016 and quarter-finalist last year, saved four match points but Pera was not to be denied and set up a meeting with Barbora Strycova when the world number 10 fluffed an overhead volley.

"I think she played very inspired throughout the whole way," said Konta.

"I think I stayed very much in the match, and I tried to find a way. I battled, and I competed. I just didn't play well enough, to be honest.

"It's a bit frustrating, but also I think I'm still taking good stuff from this. I don't feel, by any means, it's a massive catastrophe."

Goffin sent packing by veteran Benneteau

Dark horse David Goffin's Australian Open hopes went up in smoke as he fell to a 1-6, 7-6(5), 6-1, 7-6(4) to French veteran Julien Benneteau in round two on Thursday.

The Belgian seventh seed dominated the opening set in ferocious conditions but the match changed direction after 36-year-old Benneteau won the second set on a tiebreak.

Goffin was listless in the third set as Benneteau moved ahead and fell a break down in the fourth, saving a match point on his own serve at 3-5.

World number 59 Benneteau had an attack of the nerves as he tried to close out the match, throwing in a couple of double-faults to allow Goffin to level at 5-5.

But he got the job done in the tiebreak to reach the third round of a grand slam for the first time since 2013.