Ferrari's Fernando Alonso held off Red Bull's Sebastian Vettel from start to finish to win a superbly hard-fought and eventful Singapore Grand Prix.
McLaren's Lewis Hamilton failed to finish after colliding with the Red Bull of Mark Webber.
Webber went on to finish third, ahead of Hamilton's team-mate Jenson Button.
Alonso's win lifts the Spaniard to second in the drivers' championship, just 11 points behind Webber, with Hamilton nine points adrift in third.
It was a fascinating and attritional grand prix, which may have marked a decisive turning point in the world championship.
Although only 25 points cover the top five in the drivers' standings with four races remaining, the fact Alonso was able to follow his win in Italy with a second successive victory when Vettel again appeared to have the slightly faster car was significant.
It was also hugely disappointing for McLaren. Even before Hamilton's accident the British team were struggling to match their rivals for pace, and it is hard to see them closing the growing gap in time for Hamilton and Button to renew their championship challenges. Alonso acknowledged how hard the race had been.
"Not an easy race in terms of physically, conditions and also mechanically, but we tried to keep control everything, avoiding the walls," he said.
"After the first stop the race was pretty much under control. I was not too much worried about the gap with Sebastian, I was more worried about the people we were lapping."
Vettel, who is now fourth in the standings, a point behind Hamilton, was philosophical.
"I tried to push him as hard as I could, but he didn't make a major mistake," he said.
"But the most important thing is the car was competitive. Something was a bit missing yesterday [during qualifying].
"[The result] helps us in the constructors [championship], and in the drivers' everything is still open." Webber was satisfied with third after a gamble on strategy during an early safety car period paid off.
"I didn't feel mega comfortable here this weekend, so I'm very happy with how the race went," he said.
"It was easy to panic and worry about losing a lot of time behind guys. Getting out of bed this morning I would have taken third."
The fact the first five on the grid came out of the second corner in unchanged order - albeit that Alonso, from pole, mercilessly chopped across Vettel as the German closed up - did not appear to bode well for those hoping to see plenty of passing action. Their consolation was that no Singapore Grand Prix has been completed without a safety car period shaking things up, and sure enough, suspension damage forced Vitantonio Liuzzi to stop his Force India on track on lap three.
Offered a chance to gamble, Red Bull called in Webber for an immediate change from soft tyres to the harder 'prime' compound - the only one of the front-runners to pit.
The Australian rejoined in 11th, and quickly muscled his way past Virgin's Timo Glock and then, on the inside at Turn Five, Kamui Kobayashi's Sauber.
Up front, Alonso was keeping Vettel at bay, with the McLaren drivers dropping away behind them.
Webber was now some 18 seconds behind Alonso, and it was beginning to look as though the top four would be able to build up a big enough gap to pit for a change of tyres and still emerge comfortably in front.
By lap 21, Webber was almost 40 seconds behind Alonso, but the McLarens were struggling, and with the pit stops approaching, the championship leader was only 20 seconds behind Hamilton in third.
Hamilton came in on lap 29, Button on lap 30, and both were duly jumped by Webber. Red Bull called in Vettel, but Ferrari immediately responded to bring Alonso in on the same lap, ensuring he stayed ahead at the matched stop. Now it looked like a straight race to the flag, but a second safety car period - caused when Kobayashi dumped his Sauber into the railings at Turn 18 and collected Bruno Senna - brought the field back together.
The restart resulted in disaster for Hamilton. Webber was held up by a Virgin, and as he got past Hamilton closed up and began to overtake going into turn seven.
But the Englishman had not fully completed the pass when the two cars came into the corner. Webber had the inside line as Hamilton turned in, and the two cars came together.
While Webber was able to continue, the resulting damage to the McLaren - and possibly to Hamilton's world title hopes - was terminal. The stewards announced the incident would be investigated, but concluded no further action was required.
Hamilton was understandably downcast.
"I'm not really sure what happened, he was in my blind spot, I didn't see him alongside me, next thing I know is my tyre's blown and that's it," he said.
"[With not finishing at the previous Grand Prix in Italy] I couldn't have had a worse two races at this time of year. Hopefully myself or Jenson can still win the world championship."
Ahead of Webber, Vettel and Alonso were exchanging fastest laps. The gap remained constant at about a second, but the final lap saw Vettel harrying Alonso as they came up to lap backmarkers. The Spaniard made no mistake.