Title leader Jorge Martin was only 6th BUT he didn't change to new tyres doing 16 laps on the medium front and hard rear.
FP1 ends.
Francesco Bagnaia is fastest by 0.743s from Maverick Vinales.
Here comes The Maniac!
Iannone fits soft-medium tyres and takes 9th place at the end of the session!
A late fall for Pedro Acosta at Turn 9, the slow left-hander at the end of the back straight. Rider okay. Acosta is 5th on the timesheets.
Bagnaia continues his charge with the first 1m 58s lap of the weekend.
Vinales also improves but is 0.7s from Bagnaia.
Marco Bezzecchi has also put new rubber for 3rd.
Jack Miller is 4th.
Aprilia's Maverick Vinales fits new soft rubber and leaps from 19th to 3rd.
New Aprilia technical director Fabiano Sterlacchini looks on from the pits. However he's just here to observe, Romano Albesiano remains in charge until the end of the season, then joins Honda.
3mins to go.
Bagnaia 1.018s clear of Acosta, then Quartararo, M.Marquez, Bastianini, Morbidelli, Binder, Martin.
Now the lap times are getting serious: Francesco Bagnaia fits a new soft front tyre, with a medium rear, and rockets from 4th to 1st, by over 1 second, with the first sub-2minute lap of the weekend.
It's unusual for Bagnaia to go for fresh rubber so early in the weekend, but perhaps they are reacting to the threat of afternoon rain to see how the bike feels on the preferred slick tyres.
Rookie Pedro Acosta fits new medium front and hard rear tyres to climb to 2nd.
Quartararo gets a push back to the pits from countryman Johann Zarco, it's not clear if it was a technical problem or if his M1 might have again run out of fuel.
Marc Marquez, who says Sepang isn't one of his best circuits, is now the top Ducati in second behind Fabio Quartararo.
Brad Binder - who like team-mate Jack Miller sat down with Crash.net for an Interview yesterday - improves to 7th and top KTM.
Iannone is following the similar GP23 of Alex Marquez, who won last year's Sprint here and finished second to Enea Bastianini in the MotoGP.
Martin's bike snaps sideways under braking, he runs wide but no big problem.
18mins to go: Quartararo fastest from Bagnaia, Bastianini, Morbidelli, Martin, Bezzecchi, Acosta, A.Marquez, Binder, M.Marquez.
Hello... Bagnaia - presumably told Martin is behind him - pulls to the side on the back straight and slows to a walking pace. Martin dives in behind him, but Bagnaia refuses to speed up and Martin eventually overtakes, shaking his head.
Michelin's Piero Taramasso explains that riders are saving their preferred soft tyres for later in the weekend and using harder tyres this morning to clean the track.
Fabio Quartararo, who had a tough time at the February test here, continues his strong start for Yamaha by returning to the top.
At the other end of the timesheets, Iannone has reduced the gap to the top to +3.639s after just 6 laps. Impressive!
Iannone is just 0.069s slower than Aprilia test rider and Trackhouse replacement Lorenzo Savadori.
And now reigning champion Bagnaia moves to the top, by 0.145s from Martin.
...But not for long.
Martin blasts to the top on his 5th lap.
4 laps done and it's now Marco Bezzecchi quickest from Bagnaia and Quartararo.
Title leader Jorge Martin is only 15th at present.
Andrea Iannone is learning the GP23, as well as MotoGP's carbon brakes, Michelin tyres, aero and ride height devices.
The Maniac is +6.350s from the top after 3 laps.
Jack Miller, Fabio Quartararo (who has a new engine this weekend) and Joan Mir lead the timesheets after 2 laps.
Pedro Acosta reaches down and throws something from the seat of his GASGAS machine.