Starting from pole, the Spaniard had already cut the difference to Italy's Bagnaia to only eight points on Saturday with his third straight sprint victory and fifth of the season.

Ducati's Bagnaia came second in the race, giving the defending world champion 319 points compared to 316 for Martin from Ducati satellite team Pramac. Marc Marquez took third.

The 24-lap race began under overcast skies and light rain quickly intensified once the race started in mountainous Motegi.

This made for treacherous conditions with slippery turns and a sea of spray, and most riders came into the pits early on to change tyres.

Martin and Bagnaia worked their way back to the top of the field before organisers suspended the race with 12 laps to go.

They attempted a restart but the red flags quickly came out again and the riders were awarded full points according to their positions at the stoppage.

"I was committed to do a great result today," Martin said afterwards.

"I felt really good with the rear grip and I was able to overtake all of them (after the pit stop) and make this gap to win today," he added.

"I'm so so happy. Luckily everybody's away but it was too dangerous to keep going," he added.

Bagnaia said he thought he could have overtaken Martin but still appeared satisfied.

"I'm happy because it's the first time on wet that I'm doing the podium so I'm very happy," he said.

"Jorge gained some more points. But I am very happy," he said.

"Unlucky, we had (the) possibility to win. But in any case, I'm happy with the position."

Six-time world champion Marquez on Honda made his first podium finish of the year at the home circuit of the Japanese brand.

He started from the third row, but as rain caused other riders to go wide or even into gravel, the Spaniard saw an opening to race to the podium.

"I enjoyed (it). In the beginning of the race I was very calm, just tried to understand the tyres," Marquez said.

"When I saw that there was water on the track, I started to attack and I was increasing the speed step by step," he said.

Martin had already narrowed the difference to 13 points last weekend in India in Greater Noida.

This was after Bagnaia catastrophically crashed out in hot and humid conditions just over halfway through the race.

In qualifying on Saturday, Martin had set a new lap record at a dry Motegi of one minute, 43.198 seconds, followed 0.171 seconds later by Bagnaia, and 0.353 seconds by 2022 Japanese GP winner Jack Miller on KTM.

hih-stu/sco

© Agence France-Presse