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.
Source: Autosport