France's Leon Marchand delighted a raucous home crowd by setting a new Olympic record to dominate the 400m individual medley and win gold at his home Games.
The first of what the rising star hopes will be four individual golds in Paris was secured by a margin of 5.67 seconds over Japan's Tomoyuki Matsushita in second, with the USA's Carson Foster third at the La Defense Arena.
Great Britain's Max Litchfield finished fourth in the event for a third Olympics in a row, but set a new British record of four minutes 8.85 seconds.
Marchand, 22, has been one of the poster boys in the build-up to these Games and was roared home by the partisan crowd.
He finished just outside his own world record time but beat the Olympic best, previously set by American great Michael Phelps at the Beijing Games in 2008.
Ultimately, there was no contest and barely another swimmer in the frame as the 22-year-old nicknamed the "French Michael Phelps" touched the wall in four minutes and 2.95 seconds, nearly six seconds in front of Japan's silver medallist Tomoyuki Matsushita.
American Carson Foster took the bronze.
With hands on hearts, fans belted out "La Marseillaise", the French national anthem, with Marchand as he beamed atop the podium, having become the country's first medley gold medallist.
Marchand is coached in the US by Phelps' former mentor Bob Bowman, having sent a letter to the 59-year-old American prior to the last Olympics asking for help, while Phelps was in the arena to witness the win.
He will also compete in the 200m medley, the 200m butterfly and 200m breaststroke.
The French tricolores waved as he emerged into the arena but the national anthem had been belted out long before, in anticipation of this final.
As Marchand's head bobbed above the water on the breaststroke leg, the crowd roared "Allez" in unison.
It was an atmosphere like no other and the noise when he reached the finish line, for a first of what is sure to be many Olympic golds secured, was ear-splitting.
As they cheered, a crushed Litchfield lingered in the pool with his head in his hands in another agonising moment for the Briton.
