Dettori saluted the crowd and put his fingers to his lips to silence the racegoers on the Knavesmire, and persuaded Marsha assistant trainer William Butler, Lady Aurelia trainer Wesley Ward and Morris himself that he had prevailed.
Moments later Dettori discovered that the 10-11 favourite had gone down by a nose to Marsha.
"I'm in shock, I thought I'd won a neck," Dettori said later.
In light of Dettori’s unfortunate antics, Tom Peacock recalls a few instances of premature jock-elation below and some of the best examples in other sports.
Roger Loughran, Leopardstown, 2005:
Roger Loughran, who could politely be described as just above the journeyman level of jump jockeys, stood up in the irons and pumped the air when he thought that Central House had secured him a rare big-race victory in the Paddy Power Dial-A-Bet Chase at Leopardstown.
To his horror, as he eased his mount down, he realised he had mistaken the winning post by 100 yards and had to watch Hi Cloy galloping away to take the spoils.
“Roger had given the horse a super ride up till then," said trainer Dessie Hughes, in typically generous fashion.
James Ridley – Newbury 2017, Lookslikerainted:
Amateur rider James Ridley looked as if he was going to cause a 33-1 surprise in a hunter chase at Newbury in March, reaching down to give Lookslikerainted a pat with the combination well clear.
He had eased down to such an extent that his mount had stopped to a walk well before the line and was caught by the closing pack.
Not only did Ridley finish third, he was given a 28-day ban by the stewards for his troubles.
Gonzalo Higuaín, Rio de Janeiro, 2014:
As he reached forward and tapped the ball past Manuel Neuer in the 29th minute of the World Cup final, Gonzalo Higuaín wheeled away in wild-eyed celebration.
The Argentinian striker believed he had given his country the lead in the most important football match of all, only to find out the goal had been disallowed for offside.
Worst of all, Argentina were to be beaten in extra time after a strike from Mario Götze.
Luka Pibernik, Italy, 2017:
Cyclist Luka Pibernik sat up in the saddle and spread his arms out wide passing the line in stage five of the Giro d’Italia.
Unfortunately, the Slovenian had miscounted the amount of circuits of Messina and was finishing 5km too early.
The peloton caught up with the Bahrain-Merida rider and he had to settle for a far less impressive 148th position home.