In all my decades covering swimming, this evening of "Léon, Léon, Léon", the 4:02.95 Olympic-record victory, the build up to it, the crowd chorus that followed the beat of every Marchand masterstroke, rates as one of the most thrilling symphonies of swimming ever to grace an Olympic pool.

It helped to have a crowd pumped for victory and synchronising their screams and guttural, if not tribal, grunts of encouragement every stroke of the way to a victory more dominant - at 5.67sec - than even those of American medley greats Michael Phelps and Ryan Lochte when they claimed gold in dominant fashion in 2008 and 2012.

In one of the most dominant Olympic swimming victories in history, Marchand's surge was accompanied by crises of “Léon, Léon, Léon”: every stroke of the way down his eight lengths to gold just 09.45sec shy of the World record he took from Phelps last year.

After Marchand, 22, led inside world-record pace on butterfly, he turned from backstroke to breaststroke to guttural grunts that bounced off the roof and reached the French charge's ears every time he lifted his silicone-capped head to breath.

They know their swimming: it is only on breaststroke that the roar of a crowd hits home. Even the crowd lining the streets outside knew he'd gone west to seek improvement under the guidance of Phelps’ mentor Bob Bowman in Arizona for the past two years: they sang a song to the tune of "Go West", French lyrics made up in honour of a man who may emerge from a home Games with legendary status in the Olympic history of his nation.

And avatars and visualisations capturing Marchand's triumph were out there faster than you can say 'slow pool':