Bastianelli made the split to the front three riders over the Paterberg, the final major climb of the day. The Team Virtu rider was part of a select group including former Tour of Flanders winner Annemiek van Vleuten (Mitchelton-Scott) and youngster Cecile Uttrup Ludwig (Bigla Pro Cycling).
Van Vleuten tried to drop the Italian speedster a number of times, but she responded to each surge, overcoming an early sprint from the Dutchwoman to take a convincing win.
"It was really, really hard for me today," said Bastianelli. "I think it's the biggest race I have ever won and one of the most important for me. I'm really happy to have won."
Van Vleuten took second place, with Uttrup Ludwig in third who gave this entertaining speech post-race.
The 159km day started with a large breakaway shaping the course of the race. Ilaria Sanguinetti (Valcar Cylance), Severine Eraud (Doltcini- Van Eyck), Giulia Marchesini (Aromitalia Vaiano), Kylie Waterreus (Healthmate-Cyclelive), Kseniya Dobrynina (Servetto-Piumate), Silvia Valsecchi (BePink), Chanella Stougje (Hitec Products) ensured the big teams needn't worry about the break's composition.
Jip van den Bos (Boels Dolmans) and 2017 champion Coryn Rivera (Team Sunweb) were the unlucky few to not make the pointy end of the race, abandoning after crashing in the opening portion of the race.
The bunch steadily brought back the front group, making the catch 59 kilometres from the finihs. Small moves followed, but nothing stuck and the peloton gradually whittled down under the pressure.
Mitchelton-Scott worked hard break up the race, with first Sarah Roy then Amanda Spratt heading to the front, keeping the pace high. Canyon SRAM's Kasia Niewiadoma kicked off the first of the big attacks, putting a small gap into the bunch before she was brought back.
On the fabled Oude Kwaremont, it was Bastianelli who looked the strongest, on the front of the main bunch and with a dwindling group of riders who could keep up.
Uttrup Ludwig, van Vleuten and Niewiadoma proved the only ones who could hold the wheel over the top of the climb. The short gap between the Oude Kwaremont and the Paterberg changed little, but once on the Paterberg, Niewiadoma was unable to follow and the front group reduced to three, with four riders chasing behind.
With just flat terrain into the finish and a thirty second gap back to the chasing group, it was up to van Vleuten to drop the proven sprinter in Bastianelli, but the Italian proved too strong to be denied victory.