It was a session that left more questions unanswered. Although the temperatures remained as high as yesterday - 36 degrees Celsius on the track and 30 degrees air - Pirelli stuck by their mandated tyre pressures, leaving teams to wrestle with balancing set-up and tyre longevity.
Raikkonen used the supersofts for his best lap of 1m 47.974s, as did Ricciardo for his 1m 48.189s and Vettel for the 1m 48.297s lap that left him third.
Williams had an upswing in fortune as Bottas took fourth on 1m 48.504s, while Lewis Hamilton did but one lap on supersofts, which saw him cross the line with three seconds to spare before the flag fell. His 1m 48.635s left him fifth.
As expected, the world champion took yet another fresh engine this morning, making that his sixth of the season together with a sixth MGU-K, an eighth MGU-H and an eighth turbocharger. That little lot totals up to further penalties of 25 grid places, but since he already has a 30-place drop that’s a price worth paying as it gives him a pool of fresh power units to take him through the end of the season.
He spent most of the session working on race set-up on the soft tyres.
Hulkenberg in the fastest Force India took sixth on 1m 48.739s, as Rosberg was only seventh, having initially set the pace with 1m 48.742s on the soft tyre. He did not improve on that when he briefly tried supersofts.
The top 10 was completed by Williams’ Felipe Massa on 1m 48.783s, Force India’s Sergio Perez on 1m 48.915s and Haas’s Romain Grosjean on 1m 49.272s, all on supersofts.
The other big talking point was the gearbox problem which kept local hero Verstappen in the pits after only two laps. The Dutchman, fastest in FP2, faces a possible five-place drop if the gearbox requires replacement.
There were also two altercations: Manor’s Pascal Wehrlein ran off track as he moved to avoid the slow-running Haas of Esteban Gutierrez at Kemmel, and the incident is under investigation. The stewards are also looking at alleged blocking of Vettel by Renault’s Kevin Magnussen.
The fascination now will be to see whether Ferrari and Red Bull can keep ahead of a lone Mercedes when the chips are down in qualifying, when Hamilton can be expected to do minimal running in order to preserve tyres for his back-of-the-grid start.