After complaining about a s*** lap in his Ferrari, Leclerc goes again and puts in the new fastest time of the session with a 1m31.763s to go quickest.
That effort is 0.076s faster than what Norris managed a little while ago.
Wow how close can you get?
Sainz winds up a lap on softs and pumps in a time which is just 0.001s adrift of Norris's best time.
However, Norris goes for another lap and improves to move three-tenths clear.
Norris is the first driver to switch onto softs and he immediately goes fastest with a new benchmark.
It's a 1m32.165s from the McLaren driver, which sees him move half a second clear of Leclerc.
Leclerc knocks Norris off top spot with a 1m32.702s.
That puts the Monegasque fastest by nearly half a second on the hard tyre.
Norris set his quickest lap on mediums, while the other Ferrari of Sainz is third, 0.7s back.
With his McLaren teammate stuck in the garage, Lando Norris shoots to the top of the timesheet.
The title hopeful goes six-tenths clear of Mercedes' Lewis Hamilton in these early stages of FP1.
McLaren have confirmed Oscar Piastri will miss the first part of FP1 after encountering an issue with his car.
A team spokesperson said: "During this morningâs pit stop practice we encountered an issue on the rear-left corner of Oscarâs car, which we are currently replacing.
"This isnât an issue weâve seen before, but we want to assess the issue fully to ensure we have no further issues this weekend.
"We hope to get Oscar out before the end of FP1."
Green light at the end of the pit lane and opening practice is underway!
Another big talking point heading to Singapore has been McLaren's rear wing.
TV footage from the Azerbaijan Grand Prix last weekend appeared to show a part of the rear wing flexing upwards on the straight.
Baku winner Oscar Piastri insisted McLaren's car is "legal" and has passed all of the FIA's checks. F1's governing body has confirmed the wing complies with the rules but that hasn't stopped rivals from questioning it.
Red Bull's Sergio Perez described the wing as being "out of the regulations", while Ferrari's Charles Leclerc labelled it as "controversial to say the least".
One of the biggest stories heading into the weekend has surrounded Daniel Ricciardo's future.
Rumours have swirled suggesting that the Australian could be replaced at RB by Liam Lawson for the remainder of the season - following this weekend's Singapore Grand Prix.
Ricciardo admitted his future is "up in the air" on Thursday, telling Sky Sports F1: "I know how it is and how it works, and I knew there was always going to be some dates and deadlines this year, whether it was summer break or now post-Singapore, so post-Singapore is the next one.
"Honestly, it's still, so many things are up in the air. Let's see how the weekend goes. Obviously, I'm going to give it all I can, as I have. There's always something to fight for. We'll see what happens. Try to get the thing on the podium, that's my plan.â
Hello and welcome to our live coverage of the 2024 Singapore Grand Prix, which starts here!
We have two hours of practice coming up on Friday. FP1 gets underway at 10:30 BST, with FP2 taking place at 2pm.