The 18-year-old Brazilian, who is part of Fernando Alonso’s A14 Management stable, secured the championship on Friday at Monza after his title rivals failed to secure pole.
Both Prema driver Paul Aron or Campos Racing’s Pepe Marti needed to score the two bonus points for pole position to be in with a shot at the title.
But after a much-interrupted qualifying session which saw three red flags before being ended prematurely, Bortoleto was crowned champion as team-mate Oliver Goethe secured pole for Sunday’s race.
The first red flag came after Rodin Carlin driver Ido Cohen was tapped into a spin by team-mate Ollie Gray as the field bunched up in traffic.
The session was resumed before Josh Dufek, making his debut for Campos Racing, spun off at Variante della Roggia, prompting another stoppage.
Action resumed and Goethe then took provisional pole before sliding off at Lesmo 2, ending the session and handing his team-mate the title, with Bortoleto the necessary 38-points clear of second-placed Marti.
Aron finished qualifying in third, with Bortoleto fifth and Marti 16th.
Speaking to Motorsport.com, Bortoleto said: “It’s an amazing feeling, I think I will just realise maybe after the weekend is done in Monza.
“Right now I’m very, very happy, it’s a special moment for me. Rookie season and F3 winner, it’s amazing.”
He also explained why he had briefly looked confused about his title success after it was confirmed the session would not resume.
Bortoleto added: “I was talking to my coach Roberto and then suddenly he was telling me you need to improve in that or that corner and then he just did this, a sign with the hand [across his throat].
“I was like “what do you mean, a sign with the hand, to stop talking or what?” and he said “no no, it’s finished, you’re champion” and I went crazy.
“My emotions came down when I saw my whole family and the team, before that I didn’t realise I was the champion, yeah.”
The runner-up in the championship is yet to be decided, with Aron, Marti, Prema’s Zak O’Sullivan and Franco Colapinto (MP Motorsport) all within six points of each other.
The teams’ title is also yet to be secured, with Prema currently leading on 301 points ahead of Trident and Campos.
Having won the first two feature races of the season in Bahrain and Melbourne, Bortoleto went on to secure three more second-place finishes at Spielberg, Silverstone and the Hungaroring on his way to championship success.
He is now likely to graduate to Formula 2 next season as he continues his bid to become Brazil’s next F1 driver.
He is not yet a member of an F1 team’s junior academy, despite his link to Alonso.
This was Bortoleto’s maiden F3 campaign, having graduated from Formula Regional European Championship, where he finished sixth last season with R-ace GP.
He finished 15th in the championship in 2021 for FA Racing.
Prior to that, he finished fifth in Italian F4 with Prema Powerteam in 2020 in what was his first season in car racing.
