Norris, who was also fastest on Friday, looked the clear favourite for Sunday's floodlit night race after lapping the Marina Bay circuit with a time of one minute 29.646 seconds.
George Russell, who crashed his Mercedes on Friday, was 0.479 slower with McLaren's Oscar Piastri third and 0.785 off the pace.
"Lando is in a league of his own. The way he's driving his car puts it on rails," watching 2016 champion Nico Rosberg said on Sky Sports television.
"He's looking mighty out there, it's all close to perfection."
Norris is 59 points adrift of Red Bull's triple world champion Max Verstappen with seven rounds, and three sprints, remaining.
Verstappen, who has never won in Singapore and suffered his worst race weekend of the season in the city state last year, was fourth -- a big improvement on Friday -- and 0.894 slower than Norris.
The Ferraris of Charles Leclerc and Carlos Sainz were fifth and sixth, with Mercedes' seven times world champion Lewis Hamilton seventh.
Leclerc said over the team radio that he had no grip, although the conditions will be very different for later qualifying.
Williams continued to perform strongly with Alex Albon eighth and Franco Colapinto ninth. Aston Martin's Fernando Alonso completed the top 10.
