Oliveira had been excelling in the wet conditions at Motegi, rising from 16th on the grid to run as high as fourth at one stage after pitting for his wet tyre-shod bike.
The Portuguese rider started to slip backwards, but was still running sixth when he mysteriously pitted at the end of lap 12 of 24, dropping to the tail of the order.
When the race was red-flagged on lap 13 due to worsening conditions, Oliveira was not allowed to retake his position and was finally classified 18th when the race was abandoned following an attempt at a restart.
Post-race, Oliveira admitted that he chose to box because he “couldn’t see anything” in the thick spray.
“It was going well actually,” he said. “I was feeling competitive and with more rain I felt even better. The bike was handling well. But three laps before I retired I started to struggle to see.
“I couldn’t see anything, I couldn’t even see where I was going to put my wheels. There was so much water, I was telling myself not to quit and stay calm, but I came in a lap too soon.
“This never happened to me before, but I couldn’t see a thing - braking, in the corners, even trying to stay out of the spray. It was really frustrating.”
Source: Autosport