Ferrari's Leclerc sets early pace in Singapore ahead of Norris
Carlos Sainz, who won for Ferrari in Singapore a year ago, was third fastest with championship leader Max Verstappen fourth.
Leclerc lapped the Marina Bay Circuit in 1min 31.763sec on the hard compound tyre with Norris 0.076sec behind on mediums.
It was a tentative opening daylight session, unrepresentative of Saturday's qualifying and Sunday's race which will be run in different conditions under lights.
Sainz clocked 1:31.952 with Verstappen's Red Bull going around the 4.94km layout in 1:32.097.
Englishman Norris is hunting down the Dutchman Verstappen at the top of the drivers' standings.
The triple world champion's lead is 59 points with seven grands prix and three sprints to go, leaving a maximum of 207 points up for grabs.
Singapore was the only race Red Bull failed to win last year.
They returned 12 months later having lost their lead at the top of the constructors' standings at the Azerbaijan Grand Prix last weekend. McLaren are 20 points ahead after Oscar Piastri won in Baku.
The Australian may have crossed the line first there, but he was last out of the pits in Singapore and could only record the sixth-fastest time, on soft tyres.
Piastri emerged more than 10 minutes after the rest of the cars because of a problem with his left rear wheel nut becoming stuck during pit-stop practice earlier in the day.
RB's Yuki Tsunoda and Daniel Ricciardo showed promising early pace, lapping fifth and seventh fastest respectively.
Alex Albon's Williams was eighth with Fernando Alonso in an Aston Martin and Esteban Ocon's Alpine rounding out the top 10.
Verstappen won seven of the first 10 races this season but he has not triumphed in the last seven as McLaren, Ferrari and Mercedes have all taken race wins.
History suggests that Verstappen's fortunes are unlikely to improve around the unpredictable city centre track in Singapore this weekend.
Verstappen failed to make the top 10 in qualifying 12 months ago, eventually finishing fifth, and he has never won on the tight city-centre circuit.
Red Bull traditionally struggle in Singapore where tropical storms, intense humidity, concrete barriers, safety cars and red flags are ever-present dangers.
Sergio Perez did win in Singapore in 2022, but that was Red Bull's only victory here since Sebastian Vettel in 2013.
Mercedes usually fare well in Singapore, even during their recent lean years, but both Lewis Hamilton and George Russell could not get the balance right in the first session and trailed in 12th and 16th respectively.
