Karolína Plísková stunned the world number one and top seed Serena Williams in the semi-finals, winning in straight sets 6-2, 7-5 at the US Open in New York.
The Czech seed gave Williams short shrift on Arthur Ashe Stadium as the 10th seed dazzled the watching New York crowd at Flushing Meadows.
The loss sees Williams de-throned as world number one, with Germany's Angelique Kerber taking over her crown.
Pliskova reels off first set
Pliskova in her first grand slam semi-final, made a huge statement in the opening set against Serena, winning 6-2 in rapid time.
The world number one was struggling for her touch and whilst Pliskova was in total charge, on the opposite side if the net, Williams seemed woefully out of sorts and was broken in her second service game.
Pliskova was blasting returns to across the net in a display similar to her compatriot and former Wimbledon winner Petra Kvitova.
With a lead of 4-2, Pliskova took the double break advantage and held serve to take the opening set, in front of an a-gasp crowd.
In just the second meeting between the two, it was the 24 year-old from Louny in the Czech Republic who was in more immediate comfort.
Two years ago in The Bank of the West Classic, the six-time champion at Flushing Meadows won in straight sets, 7-5, 6-2. There were however no signs of that dominant display from Serena.
Czech breaks early in second
Serena was sensing an opening in the second and looked more focused on resumption.
Pliskova herself was letting errors creep in and her first serve percentage plummeted. Still the Czech scrapped and nosed reached 2-2.
The next game it was Williams who laboured. Pliskova was picking her spots against the American and at 30-40, pulled out a rapier-like forehand to force Serena long on the return and take the break. After just 47 minutes of play, Pliskova was a set and a break up.
Serena, in the history of the tournament had lost to just nine different players previously.
Williams looks for foothold
Just three game away from a major final, the reality of the occasion dawned in the spritely Pliskova. Serena broke back to love and a new sense of purpose.
But the Williams game was ill at ease. Again taken to deuce, unforced errors continue to rack up but Serena hung on gutsily, knowing she had turned around situations akin to this in her career before.
Williams began to prowl the baseline with intent but still had a mountain to climb. Both women held firm to 5-5. Serena was by now finding her range against the Czech. Pliskova, serving to save the set held on and forced the breaker.
Desperation bubbled over again for Serena, overpowering a flurry of returns, as her opponent took the mini-break to lead 3-0. The former US Open champion was given a life line as Pliskova double-faulted to 3-3.
Both women were broken with the tie-break was on a knife-edge. At 5-5, Pliskova clung on after a Williams' return was cannoned back over the net, to set up match point.
Almost as if to sum up Serena's performance, the world number one double-faulted once more, as Karolina Pliskova reached her first major final, to her own on court-surprise.
The loss for Serena means Angelique Kerber will become new world number one at the conclusion of the tournament - regardless of if she reaches the final versus Caroline Wozniacki later on.