As the final one-hour session got underway, conditions were considerably wetter than they were at the start of both FP1 and FP2, where the track was ready for slicks after a few minutes, and further rain falling at the halfway point meant the wet weather compounds were used throughout the FP3 running, other than Lando Norris completing a sole, untimed lap on softs in the final minutes.
George Russell led the pack out in the opening minutes, where the two Haas cars were the only ones to run the full wet tyres, and, despite going off into the runoff at the Bus Stop chicane ahead of starting his first timed lap, the Williams driver duly set the first place benchmark at 2m05.546s on the intermediates.
As more cars headed out and the track began to dry in places, the times steadily came down, led by Nicholas Latifi posting a 2m04.802s and Charles Leclerc – running a new chassis after his FP2 crash – putting in a 2m02.361s.
Russell then returned to the top spot with a 2m01.699s as he found time as his run continued, before Pierre Gasly moved ahead as the opening 10 minutes closed out with a 2m01.385s.
Aston Martin’s Sebastian Vettel then beat that with a 2m00.170s, before the track dried enough to bring the fastest lap benchmark under the 2ms bracket.
Hamilton was the first driver to do so, having briefly gone off at Les Combes on his first timed lap earlier in the session, a moment he repeated during the late running on a wetter track, with the world champion posting a 1m57.996s.
That stood as the best time for nearly 10 minutes before Verstappen found a big gain as his opening intermediates run went on and he set a 1m56.924s just before 20 minutes had passed.
Perez slotted in behind his teammate a few minutes later, 0.924s slower, before the rain began to fall again and times slowed as the dry line began to disappear.
This development, plus the need for the teams to save the intermediates should they be needed in qualifying, meant most drivers returned to their garages ahead of the halfway point and the on-track action was sporadic thereafter.
One driver that did run considerably once the rain had returned was Esteban Ocon, who had followed Russell out of the pits right at the start of FP3, but then spent the next 30 minutes after completing his installation lap waiting for Alpine to fix a so far unexplained problem.
But the Hungarian GP winner was able to rejoin and slot into fifth – behind Hamilton and Lando Norris, who had jumped up to fourth just before the rain fell – 1.989s slower than Verstappen’s best.
McLaren gave Norris the option to try the slicks in a late experiment with just over two minutes remaining, but the Briton returned to his garage without setting a time after touring slowly and carefully around on the red-walled softs.
Lance Stroll took sixth in the final standings ahead of Gasly, who had a late spin between the two Stavelot right handers, nearly sliding into the barriers on the inside at high speed. Vettel and Russell, with Fernando Alonso rounded out the top 10.
FP1 pacesetter, and Verstappen’s closest challenger in FP2, Valtteri Bottas, ended up down in 11th.
The Finn was another driver to slide off into the runoff at Les Combes early and he finished with a best time 2.884s slower than Verstappen.
Kimi Raikkonen brought up the rear of the field, 7.458s off the top spot and with only three laps completed, after he returned to the pits just before the 15-minute mark reporting that his brakes had failed.