British number one Johanna Konta suffered a shock defeat by world number 123 Bernarda Pera in the second round of the Australian Open.
The American won 6-4 7-5 to claim only her second win at Grand Slam level.
Ninth seed Konta had reached the quarter-finals and semi-finals on her past two visits to Melbourne Park.
“It’s a bit frustrating but I’m still taking good stuff from this,” Konta said. “I don’t feel, by any means, it’s a massive catastrophe.”
“I play every event to be there until the end, so I definitely don’t want to be going home this early.”
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Konta, 26, has now won just three of 11 matches since reaching the Wimbledon semi-finals in July.
She saved four match points on a hot and blustery afternoon but framed a smash on the fifth to give Pera the biggest win of her career.
The 23-year-old lost in qualifying and only made it into the main draw of a Slam for the first time as a lucky loser, after another player withdrew through injury.
The Croatia-born American goes on to face Barbora Strycova in the third round after the Czech 20th seed beat Spain’s Lara Arruabarrena 6-3 6-4.
‘I was a little uncoordinated today’
Konta could not cope with the pace and depth coming at her on show court two, as Pera attacked relentlessly off her returns and forehand.
The Briton’s serve failed to make its usual impact, with the average speed down 9kmph on her previous match as she finished without hitting a single ace.
Despite landing 70% of her first serves, she would end the match having won just 54% of those points, while 14 winners illustrated her struggle to hit through Pera.
“I think my serve definitely let me down a little bit today,” Konta said.
An overhead that was completely missed, followed soon after by a mis-hit smash on match point, summed up the way her game had unravelled.
“I do think I was a little uncoordinated today,” Konta told BBC Radio 5 live.
“I don’t think I’ve fallen over on my own two feet since I was going through growth spurts.”
Pera pressure too much for Konta
It was clear from the outset that Pera was going to provide a far sterner test than her ranking suggested, with a break point going begging in the first game.
A “come on!” from Konta just for holding serve at 3-3 told of the pressure that Pera was applying, and two brilliant returns gave the American the only break of the first set.
The conditions were playing their part, with Konta missing successive backhands from mid-court as the wind swirled, but two double faults in a row suggested the occasion might finally be getting to Pera as she slipped 2-0 behind in the second set.
That theory was debunked within minutes as Pera tore into another Konta service game, breaking straight back after the Briton telegraphed a poor drop shot.
Konta was under huge pressure now, battling well to save five break points before Pera made the seemingly decisive breakthrough at 4-3.
There was a final flash of resistance from Konta.
She staved off three match points and then broke to level at 5-5, but a desperate service game followed and she would end up flat on her back on the baseline as Pera broke for a fourth time.
With her game creaking, Konta’s spirit remained willing at least.
A fourth match point was seen off before Pera finally clinched the win of her life, when the Briton could only frame a smash into the stands on match point number five.
“I just didn’t play great,” Konta added. “I think it’s a part of tennis. It’s a part of everyone’s career.
“I think you can count on one hand how many perfect matches you have.
“I’d like to think as the season goes on and as I keep putting the work in, that I’ll just keep trying to find a way.”
BBC Sport tennis correspondent Russell Fuller
Pera hit nearly twice as many winners as Konta, and at times she made the ninth seed’s serve look lightweight. She was simply magnificent, and played with aggression and freedom for virtually the entire match.
There was no great spark from Konta in the first set, but she appeared comfortable enough until a barrage of winners gave Pera a love break and ultimately the first set.
Anxiety spread through Konta in the second set. She somehow lost her footing and played no shot to a Pera return which gave the American a 6-5 lead. The glare of the scorching midday sun was intense, and serves and overheads started coming off the frame of Konta’s racquet: decisively, when match point down for a fifth time.
Konta enjoyed a consistent run of success (away from the clay) for the two years after she first made a name for herself at the 2015 US Open. She has now lost eight of her last 11 matches, and along with new coach Michael Joyce has a problem or two to solve in the coming weeks.