Sainz took the lead at the Bahrain International Circuit on the second day of three days of testing, ahead of Red Bull's Sergio Perez and Mercedes' Lewis Hamilton.
The afternoon session has been moved forward by an hour, meaning a five-hour run instead of four, after two hours were lost in the morning when Ferrari's Charles Leclerc took off a drain cover while running into Turn 11.
Debris struck both the Ferrari driver and Hamilton, causing a red flag.
Bahrain Formula 1 2024 test, day two results:
What happened in Bahrain Formula 1 testing, day two?
Using Pirelli's C4 tire, which will not be available for next weekend's season-opening Bahrain Grand Prix, Sainz recorded a time of 1:29.921 seconds, compared to Max Verstappen's 1 minute 31.344 seconds from yesterday on the harder C3 compound. – which will be the designated soft tire next weekend.
Sainz's best time was 0.758 seconds ahead of Perez, who set his best time in the final 20 minutes of the session, with Hamilton a further four tenths behind – with the latter pair setting their fastest laps as the majority on the C3 tyre.
McLaren's Lando Norris was fourth, with the top four all beating Verstappen's time on Wednesday, from RB Daniel Ricciardo (on C4).
Leclerc's time since the morning was the sixth fastest time of the day, ahead of Lance Stroll (Aston Martin), Esteban Ocon (Alpine) and Valtteri Bottas (Sauber).
Despite experiencing technical problems in both sessions, which cost Red Bull some valuable time on the track, Perez recorded the most laps with 129.
What happened in the morning session of the second day of Bahrain Formula 1 testing?
Leclerc topped the morning session with a time of 1 minute and 31.750 seconds, more than half a tenth ahead of Oscar Piastri (McLaren) and Williams' Logan Sargeant.
After Leclerc hit a drain cover, red flags quickly appeared after two hours and 22 minutes of running, and after a 40-minute delay, it was announced that the session would not resume.
This was particularly bad news for Perez, who completed the fewest laps (20) of any driver after suffering a brake problem earlier that forced him to stay in the garage for more than half an hour.
Bahrain Formula 1 2024 test, results of the morning session of the second day:
| POS | driver | a team | time | gap | Rolls | Tires |
| 1 | Charles Leclerc | Ferrari | 1:31.750 | 36 | C3 | |
| 2 | Oscar Piastri | McLaren | 1:32.328 | +0.578 sec | 35 | C3 |
| 3 | Logan Sargent | Williams | 1:32.578 | +0.828 sec | 30 | C3 |
| 4 | Sergio Perez | Red Bull Racing | 1:32.879 | +1.129 seconds | 20 | C3 |
| 5 | Fernando Alonso | Aston Martin | 1:33.053 | +1.303 seconds | 31 | C3 |
| 6 | Lewis Hamilton | Mercedes | 1:33.225 | +1.475 seconds | 39 | C3 |
| 7 | Chu Guanyu | Sauber | 1:33.715 | +1.965 seconds | 38 | C3 |
| 8 | Pierre Gasly | Alps | 1:33.804 | +2.054 seconds | 33 | C3 |
| 9 | Nico Hulkenberg | Haas | 1:37.509 | +5.759 seconds | 31 | C3 |
| 10 | Yuki Tsunoda | lord | 1:38.074 | +6.324 seconds | 40 | C3 |
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