The reigning champion was an encouraging second-fastest on the opening day of the Motegi weekend, only 0.029 seconds shy of pacesetter Brad Binder on the KTM.
Both Binder and Bagnaia, as well as third-placed Aprilia rider Aleix Espargaro, eclipsed the eight-year-old Motegi lap record that was set by Jorge Lorenzo in FP2.
Having arrived in Japan off the back of a crash in last weekend’s Indian GP that has left him only 13 points clear in the title race, Bagnaia said he and Ducati were working on a solution to the braking woes that have plagued him since his last win in Austria.
The Italian rider said after Friday practice that he feels he has the Desmosedici working the way he wants again after a run of difficult races.
“I feel back on the braking,” said Bagnaia. “I can force a lot of the braking and I can take a deep breath on that because I was struggling too much on the last two race weekends, so finally I am happy for that.
“Still I am missing something to be completely happy, but it’s a huge step forward.
“On the first attempt [at a fast lap] I was doing it in a safer way, then the second one, I just pushed like I do normally and I finally felt again that I was very strong on the braking, sliding in the correct way. This is a true relief for me.”
Explaining the issue in more detail, he added: “I prefer when the bike is more stable and I control the slide more.
“The last two weekends it was too aggressive, I was sliding and losing the rear. It was very difficult to be constant on that and we improved a lot on that.”
Asked if he had returned to the set-up he used on the occasion of his win at the Red Bull Ring in August, Bagnaia replied: “The setting is similar to Austria, but not the same. We don’t know why, but this setting was not working at all [before].
“The tyres and the grip are different compared to Austria, the grip here is high and there’s a different feeling on the braking.”
Bagnaia however cautioned that Binder, who was using KTM’s new carbon-fibre chassis, will be difficult to beat this weekend at Motegi.
"The first thing I thought is that if Binder is up front, he'll be tough to beat this weekend,” he said. “We know perfectly well that if Binder starts in front, he's a really tough guy to beat."