Cian O'Connor secured Ireland's first gold medal of the Games when he won the men's showjumping final after Britain's Nick Skelton suffered a dismal finale.
The 46-year-old Skelton, the final man to jump, was going for gold but he knocked over three rails and incurred a penalty as he finished equal 11th.
That left 24-year-old O'Connor, who had burst into the lead after a perfect round on Waterford Crystal, with gold.
Brazil's Rodrigo Pessoa took the silver and America's Chris Kappler the bronze.
O'Connor was stunned at winning Ireland's first ever equestrian Olympic medal.
"I'm absolutely delighted," he said. "I never expected it. I would have been the underdog in the final.
"My horse Waterford Crystal really jumped well and the track suited me.
"You need a horse that listens to you. A lot of people were saying it would be a difficult course. I was confident enough going into the last round."
Nick Skelton missed a medal after a terrible final round
However, O'Connor revealed he will be rushing to make a few calls to Waterford Crystal's owner as the 13-year-old gelding is due to be sold after the Olympics.
Skelton has made a remarkable comeback after breaking his neck four years ago to take part in the Games.
He was firmly on course for gold after qualifying for the final round as joint-leader with Ireland's Jessica Kuerten, who also suffered in her last jump by picking up 21 penalties.
But Skelton, who was competing in his fifth Olympics on Arko III, saw his hopes vanish quickly as he picked up 13 penalty points.
The veteran said: "If he hadn't hit the triple barrier, I think we would have cleared the rest.
"But it panicked him a bit and he sat off the combination and after that it was all over.
"I have been in this game long enough and know the ups and downs. I am going to keep going on. I am not giving up. I will get there one day."
Britain's other contender Robert Smith came fifth on Mr Springfield while Ireland's Kevin Babington and Carling King secured a creditable eighth and Kuerten and Castle Forbes Maike ended in a tie for 19th.
Triple Olympic champion Ludger Beerbaum of Germany finished tied for 16th.