By winning arguably the most pressurised and challenging race of all, on the unforgiving barrier-lined streets of the principality, he proved he is a man for all circuits.
Antonelli can handle hype
Unfazed by team-mate George Russell's claim that the world title was now his to lose ahead of the race on a circuit where he finished 19th and last and was lapped three times a year earlier, Antonelli grinned, accepted the sugared barb and won.
Afterwards he jumped into the harbour and surfaced with a smile.
Seasoned observers laughed. Most Monaco winners jump into the swimming pool, not the sea; another first for the boy from Bologna. How, he was asked, does he cope with the expectation and the pressure?
"It's an incredible moment to live," he admitted. "But, of course, it's still a long season with many races to go.
"I don't want to let the pressure destroy me, like it did last year... So, I try to enjoy it as much as possible without worrying about anything else other than just driving.
"It was a good a test today with the red flag re-start - and I'm not going to lie, I was a bit annoyed because finding the mindset to re-do a full start is not easy - and I didn't fail."
As Antonelli beamed, Russell frowned. The pre-season favourite and winner of the opening race has seen his form and fortunes plummet in Miami, Montreal and Monaco.
"I am in a very, very weird state of mind because I've had low moments in my career where maybe I've had a run of two or three bad races on my own performance, but never a run of bad luck like this," he said.
Russell remains the likely main rival to Antonelli as the season unfolds.
Hamilton recovers mojo
Seven-time champion Lewis Hamilton's second straight second-place behind the driver who succeeded him at Mercedes proved that Ferrari have the potential to challenge at the front, but not the outright pace to beat the silver arrows.
As home hero Charles Leclerc endured a rare weekend of Monaco misery, with brake problems that resulted in a late crash out of the points, the 41-year-old Briton confirmed that he retains the qualities that took him to the top.
"I feel like I'm having to remind people of who I am - and now I'm showing up each weekend to do that," he said.
Penalties, retirements damage authenticity
Hamilton was one of several drivers penalised for speeding in the pit lane as the stewards impacted the race and the result with a series of penalties.
This, on top of the power-related retirements of world champion Lando Norris of McLaren and Red Bull's four-time champion Max Verstappen, plus Leclerc's late exit, produced an unexpected and strange result.
It also left many frustrated and some - including Russell and Alpine's Pierre Gasly, who was deprived of a podium after finishing third 'on the road' - angry.
It proved, however, that in the new hybrid era, reliability remains a key to success while a high level of penalties transforms the contest and raises questions about ultimate authenticity.