Outsider Harbour Law sprung a major surprise when winning an incident-packed Ladbroke St Leger at Doncaster in which the odds-on favourite Idaho fell three-and-a-half furlongs out when making his challenge.
Harbour Law is trained by Laura Mongan, who made history.
She became the first woman to train the winner of the oldest Classic, whose history dates right back to 1776
Idaho and jockey Seamie Heffernan took a nasty fall when appearing to clip heels with another runner in the race or took a false step
Idaho galloped on unscathed, while Heffernan was able to walk away apparently unhurt.
Meantime, up front a three-horse battled unfolded for supremacy.
Housesofparliament, like Idaho trained by Aidan O’Brien, kicked for home, but was soon joined by Ventura Storm.
The latter, trained by Richard Hannon, held a narrow advantage in the final furlong for champion Silvestre de Sousa, but Harbour Law (22-1) came with a wet sail to give jockey George Baker his first Classic success.
Harbour Law won by three-quarters of a length from Ventura Storm, with Housesofparliament a short head away in third.
Sword Fighter was bustled up straight from the gates to take the lead, but Muntahaa soon went on with The Tartan Spartan third, Ventura Storm fourth and Idaho well placed.
When the field turned for home with the long straight in front of them there was no hint of the drama to follow, as Idaho was just about to make his move.
However, it was not to be and it was a memorable win for Mongan and her husband Ian, a former jockey.
Jockey Baker said: “I can’t believe it.
“I am so happy for Laura and Ian because they had so much belief in the horse.
“They have done everything right - they have given him plenty of time between his races and it has paid dividends for them.
“It’s an amazing feeling.
“I worked him at Kempton about two weeks ago and he felt brilliant.
“I kind of felt we had Idaho to beat and when they had that incident, it made it a very open race.”