In an extended, stoppage-strewn race, the 19-year-old led from start to finish to claim a nerveless triumph for Mercedes that lifted him 66 points clear of seven-time champion Lewis Hamilton of Ferrari in the drivers' championship.
Hamilton, the previous holder of the youngest winner record in the principality, finished second with Isack Hadjar third for Red Bull after battling a threatened power failure all race long.
"That's too many wins now, buddy," Hamilton, 41, joked with Antonelli in the drivers' cool-down room. His own career-best run of five wins in a record total of 105 had been equalled by the Italian in his first sequence following his maiden victory in China.
For Antonelli, it was more spectacular confirmation of a prodigious talent and momentum that has catapulted him to stardom this year.
"It's been an incredible weekend and an incredible race," he said.
"It's one of those days when we had incredible pace. It was just coming all so naturally.
"The car was feeling incredible and was just giving me the confidence to push. It was a very enjoyable day.
"The job isn't finished. It's still a long season. We're going to keep pushing and keep raising the bar and try to keep performing like this."
The nerveless Italian was unfazed by the stoppages, including a standing re-start with eight laps remaining.
"To be fair, I wasn't super keen on re-starting," he said.
"Once I got away, I knew I would make it into the first corner and from that point on I enjoyed the last few laps."
On pressure, as a teenager leading the title race, he said: "I try to embrace the pressure and to use it for myself."
'We can't keep up'
Hamilton said: "I have to start by congratulating Kimi and Mercedes, my old family –- they've done it again. They've delivered an amazing car and Kimi's doing an incredible job and delivering week in and week out.
"We're progressing and can't keep up with them just yet. It's probably going to take a lot of work for us to get to their level but another second place, especially in Monaco, is a great feeling.
"It was a really challenging race, hard to stay on track with all the different things thrown at us."
Hadjar, who faced a post-race investigation into a red flag infringement, had power pick-up problems but battled through to take third with help from penalties for drivers who finished ahead of him.
He said: "It was incredibly challenging having to cover 60 laps like that and even at the end I was still lacking power at the restart.
"I was really fighting to stay within five seconds of Pierre (Gasly). For me, an outstanding weekend."
Oscar Piastri finished fourth for McLaren ahead of Racing Bulls' Liam Lawson and Arvid Lindblad.
Sergio Perez initially finished 10th, which would have earned the new Cadillac team their first point.
But he dropped down to last place after being handed a 10-second penalty for a starting box infringement.
Seven drivers, including the luckless Gasly, were penalised unexpectedly for speeding in the pit lane and had five-second penalties that affected the final result.
It was a career-best for both Racing Bulls drivers as Hamilton equalled Ayrton Senna's record total of eight Monaco podiums.
Four-time champion Max Verstappen of Red Bull suffered an engine failure at the start and retired, as did world champion Lando Norris when his McLaren had battery problems.
Source: AFP
-Agencies
