Highlights - Korean Grand Prix
Ferrari's Fernando Alonso moved into the championship lead after winning a rain-affected Korean Grand Prix.
McLaren's Lewis Hamilton was second and Ferrari's Felipe Massa came third, but Jenson Button finished 12th to all but end his hopes of retaining the title.
Alonso now leads by 11 points from Red Bull's Mark Webber, who crashed early on, and 21 points from Hamilton.
Red Bull's Sebastian Vettel retired from the lead with an engine failure and is now 25 points behind Alonso.
With only two races remaining in the season, however, Alonso insisted nothing had really changed.
"We know with the new points system everything can change in one race - if you don't score, you lose 25 points to your opponents," said the Spaniard.
"Here it was bad luck for Mark and Sebastian. Anything can happen in the next two races. As we repeat many times, being consistent is very important, we cannot forget we need to be on the podium and fighting for the victory in the last two races."
Korean Grand Prix - Top three drivers
Hamilton said it was a great result for him.
"My tyres were shot at the end, so it was just about trying to get the car home," he said.
Button, in contrast, said it had been an horrific day.
"I just didn't have any grip, and at times I was the slowest person on the circuit. Also I was just destroying tyres. It's been a sad Grand Prix."
With rain falling, race director Charlie Whiting decided the start should take place behind the safety car.
Three laps in, with Alonso describing conditions as "the worst I have ever driven in", the race was suspended and the cars returned to the grid.
After a 45 minute delay the rain had eased sufficiently for the race to be re-started, still under the safety car.
It was to be another 13 increasingly frustrating laps before the safety car finally came in at the end of lap 17.
The drama began almost immediately, as coming out of Turn 12, Webber ran wide and was unable to collect his car before spinning across the track, hitting the wall, spinning back and colliding with the unfortunate Nico Rosberg.
"Totally my fault, I got on the kerb," said the Australian. "It's frustrating, because I thought I could catch it. Conditions were fine."
It meant more work for the safety car, and the pack closed in behind Vettel. Alonso was second, ahead of Hamilton, Massa and Button.
With conditions steadily improving, Button was the first of the leading pack to switch to intermediate tyres, with a shallower tread depth for drier conditions.
He re-emerged disastrously behind a train of five midfield runners, but when Sebastien Buemi crashed his Toro Rosso into the Virgin of Timo Glock it meant another safety car period.
Vettel still led, but there was bad news for Alonso when he came in for intermediates on lap 32. A wheel-nut problem on his front right delayed the Spaniard sufficiently for Hamilton to pass him for second.
Not for long. As soon as the race resumed Hamilton ran wide through Turn 1, enabling Alonso to retake the position.
Button, still bottled up down the field, was forced wide by Force India's Adrian Sutil and lost more places on lap 36.
Up front Vettel was still in control, and Alonso responded as Hamilton began to close up.
Title not out of reach - Hamilton
With 20 minutes left on the race clock, dusk was beginning to fall as Renault's Vitaly Petrov crashed out at Turn 18.
At the front, Alonso began to close in on Vettel and the Red Bull driver predictably began to complain about the light, but he had a lot more to complain about on lap 46 when, with Alonso by now right behind him, his engine gave up in a cloud of smoke and oil.
Alonso still had Hamilton behind him but the McLaren dropped back as the Englishman's tyres began to wear more than the Ferrari's and as the darkness descended the Spaniard took both a remarkable win and the lead in the drivers' world championship.
After the race, stewards announced that Buemi and Sutil would take five-place grid penalties in Brazil for their part in their crashes. Sutil also receives a $10,000 (£6,400) fine for driving in the way he did despite knowing he had a brake problem.
Korean Grand Prix in 90 seconds