Vettel extended his championship lead with a surprisingly dominant victory at Spa, as Hamilton's Mercedes team was left struggling to explain its loss of pace.
Hamilton is under no illusions about how strong Vettel and his Red Bull are right now - but reckons that, with Mercedes having beaten its rival several times already this campaign, he can do it again.
He now trails Vettel by 58 points with eight races left.
When asked by AUTOSPORT if he felt it was now Vettel's title unless he hit trouble, Hamilton said: "It is going to be very, very tough undoubtedly.
"He has had a phenomenal car for such a long time, and it is still phenomenally quick. He does the job, so it is the perfect package.
"We have had some really strong races and been there or thereabouts competing, and finished ahead of him in the past.
"So that doesn't mean we can't do that going forwards, although it is getting closer and closer to the point where we need to finish ahead of him each and every time."
Hamilton's lack of pace in the Belgian GP was not down to the tyre issues that Mercedes had suffered from earlier in the campaign, but simply because the team's low downforce package had not worked.
"We are trying to understand where we missed out," he said.
"The guys will work out where we were slower, but Eau Rouge was particularly slow for us – as it was down the straight.
"Maybe we will be able to unlock something before the next race, but if not I am hoping Singapore will be much stronger."
Hamilton reiterated that he expected another tough time at the Italian GP, but was predicting stronger things at the end of season flyways.
"They [from Singapore] are more windy circuits, more high downforce," he said. "Coming to these two circuits [Spa and Monza], you have the downforce package and you are kind of stuck with it. It either has or hasn't worked.
"We may improve in the next race or be in the same position, but we won't be any worse.
"After that we will have the high downforce package we had in previous races or improved again. Hopefully it will be improved again."