Willie Mullins' Burning Victory won the JCB Triumph Hurdle after Goshen unseated rider when a dozen lengths clear at the final flight.
The race was billed as one of the strongest editions of the Triumph in recent years but developed into a one-horse race on the turn into the straight when Gary Moore's hugely talented Goshen shot clear with a tremendous burst of acceleration.
He only had the one flight in the straight to negotiate but clipped the top bar and agonisingly unseated the trainer's son, Jamie, who desperately tried to remain intact before crashing to the ground.
Allmankind had cut out most of the early running and he was left in front after the favourite departed, but it was the patiently-ridden 12/1 chance Burning Victory who came home best under Paul Townend to win by two and three-quarter lengths and provide Mullins with a second career success in the day-four curtain raiser.
The runner-up spot ultimately went to Henry De Bromhead's Aspire Tower, who didn't jump particularly well but stuck to his guns under Rachael Blackmore to pick up the pieces, with the tiring, Dan Skelton-trained Allmankind having to settle for third.
Fourth went to Navajo Pass for Donald McCain, while the well-touted Adonis winner Solo could never really get on terms with the pace-setters and faded up the hill to finish eighth.
Mullins said: "I just feel very sorry for Gary and Jamie. Jamie did everything right and rode the perfect race. He had the race in the bag and asked the horse all the right questions at the last, but the horse didn't answer and he just got unbalanced.
"I'm delighted we've won for our owner, but I feel hugely for Gary and Jamie - a father and son team. I know them fairly well, this was their one shot at a winner at the Festival and the work was done.
"I was just thinking of myself and Patrick and we've been there with Ruby (Walsh) as well. I know what it feels like.
"It's not a victory I'm going to celebrate hugely - we got the rub of the green."
Of Burning Victory, he added: "She's not the best jumper in the world. She jumped the first two great, but missed the two down the back and Paul knew the race was over. He was riding to maybe get into the money if he could.
"She has a huge engine and hopefully she can brush her jumping. She'll probably go back to Fairyhouse now."
Goshen is owned by Steven Packham - and was his first runner at Cheltenham.
He said: "The noise in the stand when he fell was incredible, but there we go.
"It's a massive thing to me just to have a runner at Cheltenham, as we have been coming for 30 years. I've lived and dreamt every scenario over the last month, from falling at the first, falling at the last, winning - so it has not completely surprised me.
"The main thing is that he is all right and hopefully we can live to fight another battle. He has got some engine. His cruising speed is so good. He is not flashy at home and if you saw him work you wouldn't know him from a three-mile chaser, but he just has a massive cruising speed.
"He comes into his own when he is at the track."