Jack Miller stunned the MotoGP grid on the opening day of the 2023 season on Friday as the new Red Bull KTM rider posted the record fastest time of 1:37.709 seconds during the second free practice session of the Grand Prix of Portugal in Portimao. The Australian was 12th fastest in Free Practice 1 in the morning with Gresini Racing's Alex Marquez clocking the fastest lap of 1:38.782 seconds.
Free Practice 2 saw Aprilia Racing's Maverick Vinales clock the second fastest time of 01:37.746 seconds while Ducati's reigning World Champion Francesco Bagnaia was third fastest with timing of 01:37.856 seconds. Bagnaia's teammate Enea Bastianini was 10th fastest as he clocked his Ducati the best at 01:38.2560 ahead of FP1 topper Marquez.

There were two red flags during the session as well with GASGAS' Pol Espargaro having a nasty fall following a suspected technical issue with his bike. Pol tumbled heavily before colliding into the barrier. The Spanish rider was taken to a hospital after it was reported that he suffered back and chest trauma during the mishap. The other red-flag incident saw both RNF drivers Raul Fernandez and Miguel Oliviera fall late in the afternoon.
Meanwhile, Miller's Red Bull teammate and South Africa Brad Binder was 18th fastest with a timing of 01:38.910 seconds. Mooney VR46 Racing's Luca Marini was fourth fastest at 01:37.899 secs ahead of Prima Pramac's Jorge Martin (1:37.991 secs) and Yamaha's Fabio Quartararo (1:38.015 secs) at fifth and sixth respectively.
Martin's teammate Johann Zarco was seventh fastest at 1:38.112s while Mooney's second rider Marco Bezzecchi was eighth fastest (1:38.158s) ahead of Aprilia's Aleix Espargaro (1:38.253s) at the ninth spot.
| Position | Riders | Constructors | Timing |
| P1 | Jack Miller | Red Bull KTM | 01:37.709 seconds |
| P2 | Maverick Vinales | Aprilia Racing | 01:37.746 |
| P3 | Francesco Bagnaia | Ducati | 01:37.856 |
| P4 | Luca Marini | Mooney VR46 | 01:37.899 |
| P5 | Jorge Martin | Prima Pramac | 01:37.990 |
| P6 | Fabio Quartararo | Yamaha | 01:38.015 |
| P7 | Johann Zarco | Prima Pramac | 01:38.112 |
| P8 | Marco Bezzecchi | Mooney VR46 | 01:38.158 |
| P9 | Aleix Espargaro | Aprilia Racing | 01:38.253 |
| P10 | Ennea Bastianini | Ducati | 01:38.256 |
| P11 | Alex Marquez | Gresini Racing | 01:38.385 |
| P12 | Joan Mir | Repsol Honda | 01:38.394 |
| P13 | Alex Rins | LCR | 01:38.416 |
| P14 | Marc Marquez | Repsol Honda | 01:38.419 |
| P15 | Takaaki Nakagami | LCR | 01:38.827 |
| P16 | Augusto Fernandez | GASGAS | 01:38.882 |
| P17 | Raul Fernandez | RNF | 01:38.904 |
| P18 | Brad Binder | Red Bull KTM | 01:38.910 |
| P19 | Miguel Oliviera | RNF | 01:38.958 |
| P20 | Franco Morbidelli | Yamaha | 01:38.978 |
| P21 | Fabio Di Giannantonio | Gresini Racing | 01:39.421 |
| P22 | Pol Espargaro | GASGAS | 01:40.130 |