At Roland Garros, the home of French tennis that had been transformed into a boxing arena for Olympic finals, it was more akin to Dublin than Paris.
Before Harrington and Wenlu Yang of China had even entered Court Philippe-Chatrier, you could sense there was something special brewing.
Two fights earlier, Algeria’s Imane Khelif, who put aside noise surrounding her eligibility, guaranteed herself a medal and the atmosphere was electric.
But it was about to be dialled up to 11.
Zombie by the Cranberries blared out just before Harrington entered to a sea of colour and noise.
She was cool and methodical as she strode towards the ring. It was the walk of a champion.
Fifteen minutes later, her calm exterior was shattered as the result was drowned out by a crescendo of noise from the Irish support.
While those in the stands celebrated, Harrington fell to her knees before jumping into the arms of her coaching team and then dancing around the ring.
There was even singing ringside as the Irish party was shaping up to go on well into the Parisian night.
It was an outpouring of joy and elation. Both in the stands and the ring, it was pure pandemonium.
“It was amazing. I said to the coaches after: ‘Is there anything I won’t do?'” Harrington said.
“It was brilliant. The Irish are just great. I never expected anything like that. This is something I’m never going to forget, ever.”