Before kick-off in Lille, the hosts had a ceremony for the World Cup as each player was introduced with a flag and there was a mini fireworks display in the atmospheric Decathlon Arena, which had its roof closed after heavy showers throughout the day in Lille.
While each name was cheered to the rafters when called out, the loudest, by some margin, was for Deschamps as he bid farewell to the home fans.
With the smoke from the fireworks lingering in the stadium as the game kicked off, it was Northern Ireland who settled before France gradually grew into the game.
Mbappe and Desire Doue both had half chances before Barnsley midfielder Kelly, making only his second international start, fired wide after racing onto Isaac Price's superb through ball.
Chasing Giroud's goal record, Mbappe forced a good save from Pierce Charles before he was flagged offside.
Mbappe went closer still when he tucked home Doue's cross after Tchoumeni had struck the post from the edge of the area. Doue, however, had strayed offside and the goal was disallowed.
While they dominated possession and had a goal ruled out, on the whole France's star-studded attack of Mbappe, Dembele, Doue and Olise - who had a combined 97 club goals last season - struggled to click and create many openings.
It was not the performance France had craved after their shock 2-1 defeat by the Ivory Coast on Thursday, but Olise made the difference with a statement performance ahead of the World Cup.
The opening goal was scruffy and summed up their first-half performance, but also showed the stroke of luck a team may need in a major championship.
Doue's cutback was fired towards goal by Dembele and it deflected off the unfortunate Ruairi McConville, which allowed Olise to tuck home.
Olise's second lifted the pressure within the stadium and Mbappe should have added a third, but he scooped over the bar from inside the area. The tension returned when Kelly got Northern Ireland back into the game.
Mbappe's wasted another opportunity from a tight angle as his wait continued, but Olise completed his hat-trick with a stunning strike to get the party started in Lille, and went off to a standing ovation with seven minutes remaining.
