The Mercedes driver said he was expecting a strong response from Ferrari after both Sebastian Vettel and Kimi Raikkonen went out after a crash at the first corner.
Hamilton had laboured in qualifying, starting from fifth, but he drove brilliantly in the wet and under lights to open up a potentially decisive 28-point lead over Vettel in the standings.
The 32-year-old Briton has now won the last three races, but he said there was still a long way to go with six grands prix left in the season, starting with Malaysia next week.
“Honestly, I think it’s going to be very close in the next races,” he said, warning that Ferrari would be particularly strong in Japan and Brazil. “It’s hard to predict.”
Hamilton was one of only 12 drivers to finish the first wet race on the floodlit streets of Singapore, which started with a game-changing smash and saw three safety cars.
Pole-sitter Vettel and third-placed Raikkonen sandwiched Red Bull’s Max Verstappen going into the first corner, resulting in a crash which took out all three and also ended the race of McLaren’s Fernando Alonso.
Asked whether it was karmic retribution for Azerbaijan, when Vettel finished ahead of Hamilton despite driving into him, the Briton told Sky Sports: “I don’t know if it’s karma but whatever it is I will definitely take it.”
– ‘You shouldn’t take those risks’ –
Verstappen said Vettel’s move to cut him off at the start was an unnecessary risk by the German, who held a 20-point lead in July but may now have seen his season go up in smoke.
“If you are fighting for the world championship you shouldn’t take those risks squeezing someone that much. You can see what happens,” Verstappen told Sky Sports.
For Vettel, a four-time winner in Singapore, it was a miserable night and contrasted with his joy after qualifying, when he pulled out a mesmerising lap to grab pole.
“There is nothing we can do now and for sure it is bitter, and it’s a pity we couldn’t show our pace today,” he said.
“But we have other races ahead of us and I am sure there will be more opportunities for us.”
With his 60th win, Hamilton is slowly closing on Michael Schumacher’s record of 91 — but he said the great German’s haul of seven world titles was far from his mind.
“It’s hard enough to get these championships won one at a time, it’s hard enough just to get this fourth one,” he said.
“I’m loving driving more than ever. I feel like I’m driving better than ever. I feel the most whole as a driver that I’ve ever been, which is a great feeling.”
He added that his priority this year, after team-mate Nico Rosberg narrowly beat him to last season’s title, was simple: keep errors to a minimum.
“For me (Singapore) was just about staying focused and not making any mistakes. Something I’m very set on this year,” he said.
“Coming from last year, where there were lots of mistakes, this is a year I try to make sure that, if I’m going to grow anywhere, in any space, that’s going to be it.
“And focusing on not making any mistakes seems to be working.”
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