Singapore Grand Prix winner Lewis Hamilton says he knew it would be his day when rain arrived minutes before the race.

In dry conditions, Mercedes had proven no match for Ferrari or Red Bull, but a downpour on the grid seemed sure to shake things up.

Within a matter of seconds, pole-sitter Sebastian Vettel spectacularly collided with the fast-starting Max Verstappen and Kimi Raikkonen, forcing all three to retire. 

Hamilton, who started fifth, duly swept into the lead and comfortably held off Daniel Ricciardo thereafter to take what could prove a critical victory.

"Today the miracle I needed was rain," he told reporters. "We've come here 10 years and we've never had rain on a Sunday, or even in qualifying.

"It was the first time we were all driving in the rain and when that happened I was like 'yes, it's going to be my day'."

The Briton, who was expected to relinquish the championship lead this weekend, leaves Marina Bay 28 points clear of Vettel.

"Coming here with the idea of damage limitation, thinking 'I'm going to come out of here behind in the championship again' and now I'm further ahead," he said.

"I definitely count my blessings and don't take it for granted."