Lutalo Muhammad missed out on a gold medal in the final of the -80kg taekwondo final after a last-second head shot cost him victory.
Muhammad led Cheick Sallah Cisse 6-4 with one second remaining but the restart saw the Ivory Coast fighter launch a late reverse head shot that landed on the Briton and earned him an 8-6 decision.
The London 2012 bronze medallist appeared to be well in control when he led 4-1 but Cisse levelled with a reverse body shot to make it 4-4 going into the final two minutes.
Muhammad landed a one-point kick and Cisse was given a second kyong-go penalty in the middle stages of the final round, but that was nothing on the drama that would occur in the final second.
A stoppage gave Cisse the chance to plan a last attack and it proved to be successful as his reverse kick landed on the side of Muhammad's head to spark a wild celebration from the victor, who was winning his country's first ever Olympic gold medal.
A disconsolate Muhammad had to settle for silver, to add to the bronze he won at London 2012.
"It's a horrible moment when at the last second his points have gone on the board and the time has run out and there is nothing you can do about it," an emotional Muhammad said.
"I hit him in the head and it didn't come up for me and I had to re-focus. I went to the body, I was up, and it was the last kick. My check skimmed off, and his reverse hit.
"Obviously, the emotions are very raw right now. It's tough to lose in the Olympic final, especially in the last second of a match I was winning.
"It does make it all the more painful. If I was losing throughout I would accept it, but I came very close to achieving my goal, and I am going to have to settle for second best today.
"I'm very proud to be here, a two-time Olympian and a two-time Olympic medallist - bronze, silver, so we know what's next. I'm going to take some time off and get my thinking right and I'm sure I'll be back and hungry again."