The EF Education First rider's attack came part-way up the Oude Kwaremont, quickly overhauling the escaped duo of Kasper Asgreen (Deceuninck-QuickStep) and Dylan van Baarle (Team Sky) before continuing his surge clear of the field. He maintained his lead over the Paterberg but had a task ahead of him as a strong group assembled behind.
The pre-race favourites attacked each other, hampering the pursuit of the Italian escapee, perhaps preventing the catch.
Asgreen clipped off the front of the group in a solo chase, but it proved impossible to stop Bettiol from taking the win, his first as a professional cyclist.
"I still don't believe what I did," Bettiol exclaimed. I was in Kwaremont and feeling pretty good and Andreas (Klier) from the car said if you can you just go.
"I closed the eyes and just went."
"We are a really good team and from now on you should look more in the pink at the front."
Alexander Kristoff (UAE Team Emirates) took out the bunch sprint for third, with Michael Matthews (Team Sunweb) marking his debut in the Tour of Flanders with a sixth-placed finish.
Kenneth van Rooy (Topsport Vlaanderen), Hugo Houle (Astana), Damien Touze (Cofidis), Jesper Asselmann (Roompot) kicked off the action early, the quartet forming the breakaway after a tough fight with the peloton.
Tim Declerq (Deceunninck-Quickstep) set the tempo for the bunch the lush countryside of the Flanders region. The breakaway was kept to under 10 minutes, the catch looking well assured.
Once the break was brought back within a minute, attacks started to flow from the peloton, but no one move gained too much traction.
One of the more dramatic moments of the race came as cyclocross champion and recent Dwars dor Vlaanderen winner Mathieu van der Poel (Correndon-Circus) broke his wheel and flipped over the front of his bike attempting to stop. Recovering himself, van der Poel was not only able to remount, but staged a stunning comeback into the race, rejoining the peloton and playing his part in the outcome of the race.
An attack from perrenial Flanders contender Sep Vanmarcke (EF Education First) with 50 kilometres to go was joined by Asgreen, Dylan van Baarle (Team Sky) and Stijn Vandenbergh (AG2R La Mondiale).
The attritional nature of the race began to take it's toll on the riders, Vandenbergh and Vanmarcke could no longer keep the pace at the front and numerous riders fell off the back of an already drastically reduced peloton.
With the race entering the final few climbs, Bettiol launched what proved to be the decisive attack as he pressed his bid for victory.