Petrucci was below the Assen lap record, albeit beaten by Fabio Quartararo, in FP3 with a time of 1m32.580s.
But Petrucci, like all the other Ducati riders, had a difficult qualifying session, finishing as the best of the Desmosedici riders with a 1m33.282s.
Petrucci said that in the hotter conditions of the afternoon the situation got “very difficult”.
“The problem today started in FP4 because I was telling the guys in the garage, this morning I arrive maybe one of the best bikes I ride in my life,” he explained.
“Even I used the tyre which I crashed yesterday morning. So that tyre stay 20 minutes in a field in the cold, and I was able to ride in 1m33s. Then we put a new set of tyres, and I did the lap record at the first lap.
“This afternoon, the problem was that was around 20 degrees more on the asphalt, and this situation was one of the worst of the whole season.
“Since FP4 the situation was very very difficult. In qualifying, for sure now was like a nervous qualifying, very-very because every rider is marking one another, and it’s very difficult to find a space.
“Then for sure you don’t want to be followed by other riders, but then we ride almost one second slower than this morning.
“We need to understand why, because the bike is the same but the feeling on the bike was absolutely different.”
Petrucci’s teammate Andrea Dovizioso was only 11th in qualifying, the 2018 runner-up admitting to a mistake, and also saying that Assen doesn’t suit Ducati.
“In this track where you have to change directions at high speed, it is not the best for us and every corner is very long. Is not the best for our bike,” he said. “Depends how much grip is on the track, we can be a bit faster or slower.
“In qualifying we couldn’t make a good laptime, I did a mistake so that is bad because is a bad position. Our pace is not too bad but for sure we can’t be happy.
“In the afternoon, the laptime wasn’t bad but not like the fastest. Every Ducati is not the same speed as the competitors. A bit disappointed.”