Sebastian Vettel is convinced he did not have the quickest car in Singapore after scoring his first win in five months.
Vettel beat McLaren's Jenson Button and Ferrari's Fernando Alonso to move into second place in the championship, 29 points behind the Spaniard.
The German had started from third position and moved into second at the start, but Hamilton had looked like favourite for victory until his retirement.
Vettel admitted Red Bull still needs to improve to catch McLaren, but the world champion was elated with his victory.
"We didn't have the fastest package this weekend but we still won so I am very happy," said Vettel.
"We have to improve. There is still a little bit we need to gain and at the moment McLaren is probably the fastest car and the Ferrari is a bit of an all-rounder, it is always there."
Vettel said the championship situation with six races to go looked brighter after reducing the gap to Alonso by 10 points in a single race.
"It looks better than before. Fernando finished third and it's 10 points better than before. There are a lot of races left, and it's difficult to predict what is going to happen. We have to make sure we finish the races.
"The pace is there and even if we are not quick enough to win - we have to make sure we do that. It is a tough championship so far but we are still in it."
Vettel's win was his 23rd in Formula 1, matching Nelson Piquet.