Rain hit the track at around 7pm local time in Losail, an hour before the scheduled start of the session and while the final Moto3 practice session of the day was running.
Although the rain lasted for a brief period, it left the circuit too wet to allow any MotoGP running on slick tyres, prompting race control to reduce the length of the session and not count it towards qualifying groups.
Despite the conditions being less than appropriate, the majority of the field headed out of the pitlane when the practice officially began as scheduled at 8:10am local time.
Augusto Fernandez set the early pace with a time of 2m08.974s on his GasGas Tech3 KTM, before making a number of improvements to dip well into the 2m07s bracket.
His new team-mate and reigning Moto2 champion Pedro Acosta briefly shot to the top of the times with a 2m07.441s flier, before Jack Miller became the next rider from the KTM stable to go fastest, lowering the benchmark to a 2m07.663s.
That was until Fernandez put himself back at the front, becoming the first rider to break the 2m07s barrier with a time of 2m06.938s on his GasGas-branded RC16. Acosta also managed to make a small improvement on his next flier, reinstating a Tech3 1-2 at the front of the field.
But with 20 minutes left in the session, new Gresini recruit Marc Marquez managed to find more speed on his year-old Ducati, posting a time of 2m06.544s on a still-wet Losail circuit.
His lap would remain unbeaten through the end of the 45-minute session, meaning he ended his first official day as a Ducati rider at the top of the timesheets.
Fernandez's previous lap was good enough for second, 0.290s down on Marquez, while Acosta once again finished third on what was a promising opening day for the Spaniard in both dry and wet conditions.
Miller and factory KTM team-mate Brad Binder made it four bikes from the Austrian manufacturers inside the top five, the latter ending up 0.801s off the pace in what was a largely unrepresentative session.
Trackhouse Racing's Raul Fernandez was rapid all through second practice and ended a strong sixth on the best of the Aprilia bikes, beating the top Ducati of Enea Bastianini by just under half a tenth.
New VR46 signing Fabio di Giannantonio was eighth at the end of the session, albeit another half a second down on Bastianini, with Alex Marquez next up on the Gresini Ducati.
LCR's Johann Zarco ensured Honda finished the top 10 with his best effort of 2m08.321s, despite not setting a timed lap in the first 15 minutes of the session.
He edged out the factory Honda bike of Joan Mir by just 0.006s, with Mir in turn marginally beating the works Ducati GP24 of last year's champion Francesco Bagnaia.
It was a low-key session for Yamaha, with Fabio Quartararo ending up 14th and team-mate Alex Rins propping the timesheets in 22nd place.
The factory Aprilia team likewise didn't look quick in wet conditions, with Maverick Vinales finishing a distant 15th and Aleix Espargaro languishing in 19th place. Like Zarco, both elected against setting any early laps at a wet Losail circuit.
Friday's second practice session will not count towards qualifying for the opening round of the 2024 MotoGP season. Instead, the results from final practice on Saturday will be used to determine who gets an automatic entry into Q2 and who will have to go through the first part of qualifying.
FP2, as it is officially called, will run for an extended duration of 45 minutes.
| Cla | Rider | Bike | Time | Delay | Laps |
| 1 | Marc Marquez | Ducati | 2'06.544 | 11 | |
| 2 | A.Fernandez | KTM | 2'06.834 | 0.290 | 15 |
| 3 | Pedro Acosta | KTM | 2'06.938 | 0.394 | 15 |
| 4 | Jack Miller | KTM | 2'07.263 | 0.719 | 15 |
| 5 | Brad Binder | KTM | 2'07.345 | 0.801 | 12 |
| 6 | Raul Fernandez | Aprilia | 2'07.384 | 0.840 | 9 |
| 7 | Enea Bastianini | Ducati | 2'07.436 | 0.892 | 14 |
| 8 | F.Di Giannantonio | Ducati | 2'07.997 | 1.453 | 11 |
| 9 | Alex Marquez | Ducati | 2'08.103 | 1.559 | 13 |
| 10 | Johann Zarco | Honda | 2'08.321 | 1.777 | 12 |
| 11 | Joan Mir | Honda | 2'08.327 | 1.783 | 12 |
| 12 | F.Bagnaia | Ducati | 2'08.494 | 1.950 | 12 |
| 13 | Marco Bezzecchi | Ducati | 2'08.648 | 2.104 | 14 |
| 14 | Fabio Quartararo | Yamaha | 2'08.702 | 2.158 | 12 |
| 15 | Maverick Vinales | Aprilia | 2'08.839 | 2.295 | 9 |
| 16 | Luca Marini | Honda | 2'09.184 | 2.640 | 13 |
| 17 | F.Morbidelli | Ducati | 2'09.399 | 2.855 | 16 |
| 18 | Jorge Martín | Ducati | 2'09.495 | 2.951 | 13 |
| 19 | Aleix Espargaro | Aprilia | 2'09.777 | 3.233 | 13 |
| 20 | Miguel Oliveira | Aprilia | 2'09.813 | 3.269 | 13 |
| 21 | Takaaki Nakagami | Honda | 2'10.350 | 3.806 | 14 |
| 22 | Alex Rins | Yamaha | 2'10.535 | 3.991 | 14 |
