How it unfolded
Senna had to win to take the title. He took pole but stalled at the start and dropped to 14th. Suzuka's downhill grid let him bump-start the engine — terrain that saved his championship. Prost led ahead. Senna passed multiple cars on lap one, reached fourth before lap 10 and second by lap 20. Light rain then favoured him. He passed Prost at the chicane mid-race and pulled away to win by 13.4 seconds and become world champion. That year the McLaren MP4/4 won 15 of 16 races; Senna took eight wins, Prost seven. On total points Prost led 105-94, but under the rule counting only the best 11 results, Senna won 90-87.
Why it still matters
This is where F1's greatest rivalry officially began. Two champions in the same car clashed at Suzuka in 1989 and 1990 as well; managing teammates became every top team's permanent problem. Senna's recovery drive showed one bad start need not end a season, and the controversy over dropped scores helped push the sport toward counting every round.