Bagnaia: 'I have a lot of questions about my race'
A strong wet rider, the torrential rainstorm that delayed the start of the grand prix didn't dampen Bagnaia's hopes of a high-scoring result.
But while reigning champion Quartararo rode to second place behind Miguel Oliveira, Bagnaia was in big trouble from the 'first braking'.
The Italian eventually dropped all the way from sixth on the grid to 15th at the flag.
Combined with an accident while fighting over eighth place in Qatar, Ducati's title runner-up has taken just one point from a possible 50 in the opening rounds.
"I'm quite disappointed, for the second weekend in a row," Bagnaia said. "We took just one point in two weekends.
"Our potential is a lot higher and this morning with used [dry] tyres I was eleventh in warm up but my pace was very, very competitive.
"I was ready again to fight for the win with Fabio because my feeling was incredible, but the result was the total opposite. So it's a difficult situation."
Bagnaia simply didn't have the pace in the wet race, his best lap also only 15th fastest and some 1.6s behind not only Quartararo but the fastest Ducati lap by Johann Zarco (Pramac).
"I have a lot of questions about my race," Bagnaia said. "Because it's strange that in the test in Malaysia I had a really great feeling in the wet, in the test here in the first session I was very strong in the wet and my feeling was incredible like always. And today, I was struggling a lot from the start.
"Already from the first braking in the race, I was feeling strange. I lost a lot of positions. Then when I was trying to push a bit more, I was always losing the front."
That included saving a big moment under braking for turn one, which sent the Italian off track. "I had the luck to not crash at the end of the straight because I was going quite fast and it was a bit scary," Bagnaia said.
"But looking also at the tyre, it was not working. So maybe I was not pushing like I need to do, but it looks strange."
While reluctant to point the finger directly at his front tyre performance, Bagnaia seemed to rule out a bike or setting issue.
"For me, the problem was not my bike," he said. "Because in the wet our bike is incredible, and for me, today, it was not like this. I was struggling too much with one of the strong points of our bike in the wet, which is the front."
One of the big talking points during the Mandalika weekend was a revised rear casing for the Michelin slick tyres, which seemed to suit the Ducatis quite well, but the wets were of the usual design.
"Normally you have one wet bike setting, made for these tyres, that normally works well every time, so we didn't change anything," Bagnaia confirmed.
"I'm not saying that it was a problem with the tyre, I'm just saying that it was not working like I want. My feeling with it was very strange. Normally, I'm very sensitive about the limit of the front tyre. And today, that was not the situation.
"When I locked the front [into Turn 1], I was not braking very strongly. Jack [Miller] was doing stronger braking than me, and I was just understanding the situation, because I was going slow.
"But I was on the limit with the front, because I was not understanding what was happening, and when you feel like this, it is very difficult to push. On TV you have just seen one front locking, but it was not just one. And also inside the corner I was losing it a lot of times. It's strange, I think."
The only positive for Bagnaia was that, after a tough opening weekend in Qatar where he 'lost' valuable race preparation time testing new parts, he had been feeling 'incredible' with the new GP22 after warm-up in Mandalika.
"It's just the second race. We are understanding things, and like I said before, my feeling this morning was incredible with the bike. So we were ready to fight for the win," Bagnaia said.
"Let's see for the future in the next races, but I would like to reset my mindset and start again thinking positive, and don't think to be unlucky always."
Team-mate Jack Miller completed Sunday's podium in third place.
Bagnaia will head to next weekend's Argentine round 29 points behind early title leader Enea Bastianini (Gresini Ducati).