The Italian set a 2m00.295s on his final attempt to top the timesheet, with Marini just 0.036s behind him.
Bezzecchi, who sits second in the championship standings after the summer break, set an early benchmark of 2m04.821s to lead early on, improving to a 2m00.885s on his fifth lap.
That lap remained quickest for much of the session, before Marini went faster with five minutes left, just five-thousandths of a second better than Bezzecchi.
But Bezzecchi went faster still on his final flying lap, topping the timesheet as he hopes to continue his strong form, having taken a sprint race win and second place in the grand prix at Assen last time out.
The VR46 Ducati pair led from the Pramac duo of Jorge Martin and Johann Zarco, with just two-tenths separating the top four.
With FP1 no longer counting towards Q1 and Q2, it was a more sedate start to the session than usual.
Bezzecchi set an early benchmark before it was bettered by Martin, with a 2m04.506s going quickest as Aprilia’s Maverick Vinales slotted into third.
KTM factory rider Jack Miller went top next, with a 2m02.808s, 0.09s quicker than Bezzecchi in second.
Source: Autosport