The Red Bull was the class of the field at last weekend's Japanese Grand Prix and Vettel took full advantage, completing the clean sweep of pole position, fastest lap and race win.
On current form, it is difficult to see Alonso and Ferrari being able to fend off Vettel and Red Bull. But despite taking his third win of the season and second in succession, Vettel does not consider himself favourite as all eyes now turn to this weekend's event in Korea.
He said: "I'm very careful. I think we have had a long journey so far, and it's been a tough year.
"Still there are many races to go, so I don't want to talk about the championship.
"I know I finished in front of everyone. I won the race, so I know that I scored more points than anybody else here but you don't know what happens next weekend.
"I think we have a very tough remainder of the season with a very new calendar for all of us, with a lot of back-to-back races.
"Basically Korea, then two races, one in India and Abu Dhabi, and then obviously America and Sao Paulo.
"I think there's still a long way to go and, as I said, we have to focus on every single race and try to do our best and then we will see whether it's good enough."
Alonso, for his part, tried to stay upbeat despite seeing his handy lead of 29 points all but erased in one fell swoop.
He said: "This result has practically wiped out the advantage I had before, but if I'd been told at the start of the season that we would have been in this situation five races from the end, I'd have taken it.
"We must work a lot on the development of the car. I'm not worried, but we must react to the step forward that the other competitors have made."