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 and preventing an all-Williams sisters final at the Dubai Open.
The 24-year-old Frenchwoman, who is about to return to the 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 throughout an extraordinary second set.
She rode the momentum she had created to break again for 2-0, and although Serena pulled that break back, she was increasingly tense, dropping serve again to go 3-4 down in weird circumstances.
Firstly she put an uncharacteristic and inappropriate drop shot into the net, then she failed to run a return of serve down, wrongly thinking her first delivery had been out - Hawkeye proved it wasn't - and then on game point she made a gambler's rush to the net. Cornet passed her almost dismissively.
Eventually came Serena's last card - her renowned capacity to fight. Sure enough, she saved the four match points at 5-3, but it only delayed the end against an adversary as self-possessed as this.
At the moment of truth, seeking to close out the match, Cornet cut down the pace on her first serves and got them all in. That gave her enough psychological advantage to force further Serena errors without needing heroics.
"Nothing was on my mind when I served for the match," Cornet said. "It was like OK, don't worry. I thought 'you're a big girl, you can do it'. And I did. It feels amazing."
Earlier, Venus Williams had raised the possibility of an all-Williams sisters final for the first time in more than four years when she scored her fourth win of the week.
Her 6-3, 6-2 win over Wozniacki saw her dominate the former world number one from Denmark 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. Serena is 32 and it remains to be seen how much her fitness problems and absence of results this year have become a function of the passing years.
Cornet meanwhile seemed sure the future belonged to her. Asked if she could now win the title, she said: "I hope so. Venus is a great player - but now I have beaten the better of the sisters, so maybe I can do it."