The Red Bull driver and his Ferrari rival arrive at this weekend's Korean Grand Prix separated by just four points following Vettel's win in Japan and Alonso's failure to finish.
Hamilton lies fourth in the standings, 42 points adrift of Alonso, but could have been so much closer had his gearbox not failed while he was leading in Singapore.
The McLaren driver has played down his chances of landing his second title before he departs for Mercedes at the end of the year, and needs to turn around a difficult Suzuka weekend, where he finished fifth, if he is to keep himself in the frame over the final five races of the season.
But Alonso and Vettel are not of the opinion that they are locked in a private battle for the championship.
Vettel said: "I think they (McLaren) are still fighting for the championship. I think that is their target, or has to be their target.
"I think if you look at the races we had after the summer break, so far, if you summed them up, on average I think McLaren was the most competitive car.
"They are the ones which will be very competitive, no matter where we go, at least that's what the last couple of races showed. I think they still have a good chance."
Alonso added: "I think it is more difficult for him as it is not only one driver ahead that you need to take some points off.
"We are now two drivers with more or less the same points ahead and he is behind, so for sure the chances for him are a little bit lower.
"But if we see the form of McLaren and Lewis before Suzuka there is still plenty of time and points to do it, he still has the possibility."