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.
Either 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.
Source: Autosport