Coming from behind after an Ivan Perisic opener at San Siro, 35-year-old Giroud has once again proved his worth since moving to Italy as he helped Milan reduce Inter's advantage at the top of Serie A to just a single point.
Perisic opened the scoring as he superbly vollied in a Hakan Calhanoglu corner to put the league leaders in the ascendancy.
And Liverpool's Champions League last 16 opponents, Inter, dominated much of the first hour of the game, putting Milan goalkeeper Mike Maignan under intense pressure, but then the Giroud show began.
It wasn't without controversy though, with Giroud barging over former Arsenal teammate Alexis Sanchez on the halfway line to win back possession in the 74th minute.
The ball was then carried forward and offloaded to Real Madrid loanee Brahim Diaz, whose blocked shot looked to be heading wide before Giroud stuck out one of his long legs.
VAR allowed the goal to stand with Inter fuming, but they failed to get their heads back in the right space and a few minutes later Giroud was back at it.
Collecting a rather harmless looking Davide Calabria pass inside the penalty area, Giroud then spun Stefan de Vrij all the way back to the Netherlands before steering the ball in.
The moment was so big that it sent Milan's usually calm and collected manager Stefano Pioli running like crazy to celebrate with his players under the Curva Sud.
The magnitude of the three points was then put on show in stoppage time, with Inter's Denzel Dumfries set to breakaway on the right hand side, Milan's Theo Hernandez was happy to hack the Dutchman down for a red card.
Often criticised for not being an out-and-out goal-scorer and taking Karim Benzema's spot for the French national team, Giroud is now a Champions League and World Cup winner.
'Giroud, you are they derby,' read La Gazzetta dello Sport on Sunday morning, and you'd imagine this is far from the last time he decides yet another big game.