Alize Cornet, recovering brilliantly from a mighty collapse in career fortunes, scored her best-ever win by beating world number one Serena Williams 6-4 6-4 to prevent an all-Williams sisters final at the Dubai Open.
The 24-year-old Frenchwoman, who is about to return to the WTA's top 20 after a dismal five-year interval in which she fell from the top 100, made a mere handful of errors as she manoeuvred and harassed the legend to a stunning defeat.
Cornet often rallied valiantly when the powerful American landed her biggest blows, but even more often she found changes of direction and angles to disrupt Serena's rhythm.
That this happened more often than usual to the favourite was unsurprising considering that this was her first tournament since injuring her back in last month's Australian Open.
Serena later pronounced herself "a wee bit embarrassed" by the result, which denied her the chance of a final with older sister Venus Williams, an earlier winner against Caroline Wozniacki.
She also had a fit of incongruous laughing as she claimed that she had "not made that many errors in a match in, I think, at least three years, maybe four years", and had not felt good all week.
In truth, Serena did enough to have beaten most other opponents. But this one was unusually smart and courageous as well as skilful and level-headed, and took her rare opportunity with tremendous panache.
"It's my best ever win - but I haven't realised it yet," Cornet said, still hopping up and down with joy during the on-court interview.
"I played a very good match. Most of the time I didn't even realise who I was playing, and that's the way I had to be. I had to forget it was Serena on the other side, and just get on with my game."
Cornet also seemed to have an instinct which made her do the right thing at the most important moments, and crucially she changed the mood of the match when she broke Serena's serve at 4-4.
She did that by taking advantage of a couple of Serena errors by immediately lifting her level, finding some great variations to get back from 40-15 down. After reaching 5-4, she closed out the set without fuss.
After that, the pressure was suddenly on Williams, and Cornet managed to keep it there.
Earlier, Venus Williams had raised the possibility of an all-Williams final for the first time in more than four years when she scored her fourth win of the week 6-3 6-2.
She dominated former world number one Wozniacki from start to finish with her heavier, and sometimes cleverly angled, driving.
Once again it suggested that 33-year-old seven times former Grand Slam champion, who is still ranked outside the top 40, may be making her way back - after prolonged health problems - to a position where she could be seeded in major events.
Venus had, she said, really been looking forward to playing Serena again - almost, it sounded, as if for old times' sake.