Andrea Dovizioso won the final race of the MotoGP season as 13 riders failed to finish a wet Valencian Grand Prix.
Ducati's Italian rider, 32, finished well ahead of Suzuki's Alex Rins, with Rins' fellow Spaniard Pol Espargaro securing his first podium finish.
Dani Pedrosa, 33, was fifth in his final GP before retirement, in a race halted for 30 minutes due to the rain.
Marc Marquez, who secured a fifth world title in October, pulled out having gone over his handlebars early on.
Yamaha's seven-time world champion Valentino Rossi was another high-profile faller, with his late exit allowing Espargaro to take second place.
Rossi, 39, still finished third in the 2018 championship standings, behind Marquez and Dovizioso.
Yamaha's Maverick Vinales started on pole but quickly surrendered his advantage to Rins, who went on to lead for the majority of the race.
That included after a red flag reset the race to lap 13, as heavy rain made the conditions too dangerous to continue, before Rins was overtaken by Dovizioso and Rossi.
"It was a crazy race," said Dovizioso after securing his fourth race win of the season. "I am proud not to crash because there was too much water.
"After the restart we made some changes on the bike, we put on new tyres and I felt so good. It's a nice feeling to finish the championship like this."
Pedrosa, a three-time championship runner-up in 2007, 2010 and 2012, equalled his best finish of 2018 to end the season 11th in the standings with 117 points.
The Spanish rider bows out with 31 wins from 216 starts having spent his entire 13-year MotoGP career with Honda.
1. Andrea Dovizioso (Ita/Ducati) 24mins 03.408secs
2. Alex Rins (Spa/Suzuki) 24:06.158
3. Pol Espargaro (Spa/KTM) 24:10.814
4. Michele Pirro (Ita/Ducati) 24:12.055
5. Dani Pedrosa (Spa/Honda) 24:16.759
6. Takaaki Nakagami (Jpn/Honda) 24:35.696
7. Johann Zarco (Fra/Yamaha) 24:36.214
8. Bradley Smith (GB/KTM) 24:36.519
9. Stefan Bradl (Ger/Honda) 24:39.784
10. Hafizh Syahrin (Mal/Yamaha) 24:40.606
Final championship standings
1. Marc Marquez (Spa/Honda) 321pts
2. Andrea Dovizioso (Ita/Ducati) 245
3. Valentino Rossi (Ita/Yamaha) 198
4. Maverick Vinales (Spa/Yamaha) 193
5. Alex Rins (Spa/Suzuki) 169
6. Johann Zarco (Fra/Yamaha) 158
7. Cal Crutchlow (GB/Honda) 148
8. Danilo Petrucci (Ita/Ducati) 144
9. Jorge Lorenzo (Spa/Ducati) 134
10. Andrea Iannone (Ita/Suzuki) 133