Teams were braced for inclement weather, with thunderstorms fast approaching Barcelona from the Pyrenees in the north.
The session started on dry-weather tyres, but spots of rain were soon reported around the Circuit de Barcelona-Catalunya.
That completely disturbed the teams' usual run programmes in FP3, with all drivers rushing out of the pits at the drop of the green flag to get some precious dry running in.
Most drivers went straight to a single-lap timed run to prepare for qualifying, with Red Bull's Verstappen's 1m13.664s leading team-mate Perez by 0.250s and Mercedes duo Lewis Hamilton and George Russell slotting in behind them.
Home heroes Carlos Sainz and Fernando Alonso soon split the Mercedes drivers, taking fourth and fifth respectively.
The predicted rain showers duly arrived at the 10-minute mark, hitting the restored final sector first.
Williams' Logan Sargeant appeared to be caught out by moisture in the now ultra-fast final righter-hander, initially correcting a slide but then veering off into the gravel.
Sargeant got away with minimal left-hand side damage as he gently tapped the wall, but as the rain intensified the red flag put paid to any more improvements.
After a nine-minute delay the session was green-flagged again, but it took until hast the half-hour mark for drivers to sporadically venture out on a damp track.
McLaren's Lando Norris took on the task of conducting a reconnaissance lap on the intermediates to check out the conditions, while the rain appeared to ease off.
With 22 minutes to go most other drivers followed Norris' example as any intermediate running could prove of great value for Saturday afternoon's qualifying and for Sunday's grand prix, with more potential rain on the way.
In the final minutes Lance Stroll made an excursion through the gravel at Turn 6 on intermediates and Pierre Gasly slid off at Turn 7.
Meanwhile, several others returned to Pirelli's soft slicks, getting close to dry weather times at the end.
Despite the first two sectors drying up, Verstappen's time at the top was never in doubt, heading Perez, Hamilton, Sainz and Alonso.
Russell was sixth ahead of Leclerc, with Alfa Romeo's Valtteri Bottas, AlphaTauri man Yuki Tsunoda and Norris rounding out the top 10 after single hot laps in the dry.
Zhou was 11th for Alfa Romeo, followed by Nyck De Vries, Aston Martin's Stroll and the first Haas of Nico Hulkenberg in 14th.
Oscar Piastri was 15th for McLaren ahead of Esteban Ocon in the first of the Alpines. He headed and Kevin Magnussen, Pierre Gasly as Williams duo Alex Albon and Sargeant propped up the timesheets.
F1 Spanish GP: Full FP3 results
| Cla | Driver | Chassis | Engine | Time | Gap | |
|---|---|---|---|---|---|---|
| 1 |
 Max Verstappen |
 |
Red Bull | Red Bull | 1'13.664 | |
| 2 |
 Sergio Perez |
 |
Red Bull | Red Bull | 1'13.914 | 0.250 |
| 3 |
 Lewis Hamilton |
 |
Mercedes | Mercedes | 1'14.072 | 0.408 |
| 4 |
 Carlos Sainz |
 |
Ferrari | Ferrari | 1'14.240 | 0.576 |
| 5 |
Fernando Alonso |
 |
Aston Martin | Mercedes | 1'14.264 | 0.600 |
| 6 |
George Russell |
 |
Mercedes | Mercedes | 1'14.278 | 0.614 |
| 7 |
 Charles Leclerc |
 |
Ferrari | Ferrari | 1'14.353 | 0.689 |
| 8 |
 Valtteri Bottas |
 |
Alfa Romeo | Ferrari | 1'14.360 | 0.696 |
| 9 |
 Yuki Tsunoda |
 |
AlphaTauri | Red Bull | 1'14.659 | 0.995 |
| 10 |
Lando Norris |
 |
McLaren | Mercedes | 1'14.681 | 1.017 |
| 11 |
 Zhou Guanyu |
 |
Alfa Romeo | Ferrari | 1'14.681 | 1.017 |
| 12 |
Nyck de Vries |
 |
AlphaTauri | Red Bull | 1'14.693 | 1.029 |
| 13 |
 Lance Stroll |
 |
Aston Martin | Mercedes | 1'14.756 | 1.092 |
| 14 |
 Nico Hulkenberg |
 |
Haas | Ferrari | 1'14.988 | 1.324 |
| 15 |
 Oscar Piastri |
 |
McLaren | Mercedes | 1'15.105 | 1.441 |
| 16 |
 Esteban Ocon |
 |
Alpine | Renault | 1'15.266 | 1.602 |
| 17 |
 Kevin Magnussen |
 |
Haas | Ferrari | 1'15.534 | 1.870 |
| 18 |
Pierre Gasly |
 |
Alpine | Renault | 1'15.841 | 2.177 |
| 19 |
 Alex Albon |
 |
Williams | Mercedes | 1'15.851 | 2.187 |
| 20 |
 Logan Sargeant |
 |
Williams | Mercedes | 1'16.529 | 2.865 |
| View full results | ||||||
