He goes sixth in the Haas, 1.8s shy of Sainz's top time.
Hamilton slots into third overall on the C5 tyre (the softest compound available), 0.752s off Sainz's C3 benchmark from earlier.
Looks like he was preparing a quick lap but ran wide at Turn 1 after a small front-right lock-up.
1. Sainz - 1m32.247s - C3
2. Perez - 1m31.647s - C3
3. Norris - 1m32.108s - C3
4. Stroll - 1m32.361s - C3
5. Hamilton - 1m32.902s - C3
6. Albon - 1m33.093s - C3
7. Magnussen - 1m33.273s - C3
8. Bottas - 1m33.690s - C3
9. Ocon - 1m33.965s - C3
10. Ricciardo - 1m38.044s - C3
Perez improves his lap time to a 1m31.647s, 0.400s off Sainz's top time from earlier. A few others are also finding time with Albon and Magnussen slotting into sixth and seventh respectively.
Perez sets a 1m37.788s to slot into second, 0.5s shy of Sainz.
Norris is currently third-quickest, 0.861s off the top time.
All of the running is being done on the C3 tyre - the compound which will the soft tyre next weekend.
Hamilton's first representative time of the day puts him fourth, 1.6s off the pace.
Hamilton leads Sainz out of the pit lane as Day 3 gets back underway.
The session will resume in three minutes - and will run until 4pm UK time.
No lunch break.
Repairs to the track are ongoing.
Looks like there will be no lunch break with the test running from now until 4pm UK time.
"Estimated start time is 8:45 UK time - to be confirmed"
No change to the situation with three hours on the clock.
Circuit officials are still repairing the loose drain cover on the approach to Turn 11.
- Sainz - Ferrari - 1m31.247s - C3
- Norris - McLaren - 1m32.108s - C3
- Albon - Williams - 1m33.848s - C3
- Perez - Red Bull - 1m34.790s - C3
- Magnussen - Haas - 1m36.049s - C3
- Hamilton - Mercedes - 1m37.772s - C3
- Ricciardo - RB - 1m39.507 - C4
It looks like Perez was the one who dislodged it after going slightly wide at Turn 11.
Everyone is back in the pit lane as we await an update from race control.
The drain cover on the approach to Turn 11 has come loose.
The session has been halted. Let's hope it's a quick turnaround.
Sainz moves onto the C3 tyre and finds more time, extending his advantage to 0.8s over Norris.
A 1m31.247s for Sainz. Just before that, Norris had improved as well, but someway off his former teammate.
1. Sainz - 1m32.017s - C4
2. Norris - 1m33.742s - C3
3. Albon - 1m33.848s - C3
4. Perez - 1.35.510s - C3
5. Magnussen - 1m36.049s - C3
6. Hamilton - 1m37.772s - C3
7. Ricciardo - 1m39.507s - C4
Continuing on the C4 tyre, Sainz sets a 1m32.017s to move 1.7s clear of his nearest rival.
The Spaniard already has six laps on the board - the most of any driver so far this morning.
- Sainz - Ferrari - 1m32.737s - C4
- Norris - McLaren - 1m33.742s - C3
- Albon - Williams - 1m34.745s - C3
- Perez - Red Bull - 1m35.510s - C3
- Magnussen - Haas - 1m36.583s - C3
- Ricciardo - RB - 1m42.316s - C4
Some early times are already on the board with Sainz running on the C4 tyre - setting a 1m32.737s, 1.0s clear of Norris' C3 lap.
Albon is 2.0s off in third, also on the C3 tyre.
Stroll and Magnussen are the first drivers out on track as the final day of testing gets underway at the Bahrain International Circuit.