The 26-year-old's third successive Korean win, and eighth triumph in 14 races, left him 77 points clear of Ferrari's Fernando Alonso with five races - and a maximum 125 points -remaining.
If the German wins in Japan next weekend - as he did last year - and Alonso fails to finish in the top eight - as also happened last year - the championship will be over.
"That was a very, very disciplined drive. Well done," team principal Christian Horner told him over the radio after taking the chequered flag. Vettel, who now has 34 career wins, replied with his customary whoop of delight.
Alonso could manage only sixth place on an overcast afternoon that threatened rain without delivering the downpours that might have mixed up the field and given him more of a hope. The Spaniard now has 195 points to Vettel's 272.
"There's still a chance for Fernando, I think," said Vettel. "So we have to stay on top of our game. But to be honest...we're just having a good time.
"I look forward to Japan because it's one of the nicest tracks of the whole season."
In a race that exploded into action, with two safety car periods including one bizarre moment when a fire marshals' regular 4X4 drove on to the track and led the field before the official Mercedes pace car had been deployed, Vettel celebrated his fourth victory in a row.
Finland's Kimi Raikkonen finished second, ahead of Lotus team mate Romain Grosjean, in a race running along familiar lines of Vettel domination before jolting the audience awake with a bang.
McLaren's Mexican Sergio Perez brought out the first safety car with the explosive delamination of his front right tyre, which had worn through after hard braking, that left a strip of tread lying in the middle of the track on lap 31 of 55.


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