Serena Williams became the most high-profile casualty at the Australian Open so far after suffering a shock last-16 defeat by unseeded Ekaterina Makarova.
The 13-time major champion - a five-time winner at Melbourne Park - made 37 unforced errors as 56th-ranked Makarova won 6-2 6-3 in 82 minutes.
"I don't know what to say. It's an amazing feeling," said Makarova.
In her first Grand Slam quarter-final, the Russian will play compatriot Maria Sharapova or Germany's Sabine Lisicki.
The result ended Williams's 17-match Australian Open winning streak.
The American, seeded 12th after an injury-hit 18 months, and absent from last year's tournament, had not lost in Melbourne since a defeat by Jelena Jankovic in 2008.
It was was her first loss to a player ranked outside the world's top 50 in three years and only the third time since 2006 she had lost before the quarter-finals of a Grand Slam.
A lack of match fitness seemed to catch up with Williams in the blistering heat and she was second best throughout as Makarova claimed a richly deserved victory.
She broke for a 3-2 lead in the opening set and then again for 5-2 as Williams's usually dominant serve faltered badly.
Williams improved at the start of the second set as she claimed a 2-0 advantage, but Makarova broke back immediately and then moved 3-2 ahead when her opponent double-faulted a remarkable four times.
The momentum remained with Makarova and despite squandering three match points, she came through on a fourth when Williams sent a tame backhand into the tramlines.
"She is an unbelievable player and it is very tough to play her," the Russian added.
"It was tough - it is a big stadium and an unbelievable feeling. I am just happy."
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