Watch: Vettel completes Ferrari sweep of Belgian practice
Ferrari's Sebastian Vettel closed out Belgian Grand Prix practice with the fastest lap on Saturday ahead of team-mate Kimi Raikkonen.
Championship leader Lewis Hamilton was third quickest for Mercedes, 0.137 slower than his German rival's best of one minute 42.661 seconds in the third and final session, on an overcast and damp morning in the Ardennes forests.
Hamilton, last year's winner in Belgium, is 24 points clear of Vettel with nine races remaining but the Ferraris look strong and have led every single practice – Vettel the first on Friday and Raikkonen the second.
Vettel was 0.063 quicker than Raikkonen in the third session.
Stoffel Vandoorne provided the main talking point, the Belgian blaming Hamilton's team mate Valtteri Bottas for an incident that squeezed the McLaren on to wet grass before it spun across the track and into the barriers.
"What the hell was the Mercedes doing?" exclaimed Vandoorne, who ended at the bottom of the timesheets, over the team radio as red flags came out to halt the session. "He just pushed me onto the grass."
Bottas, who will start at the back of the grid due to engine penalties, said he had not seen him.
Red Bull's Max Verstappen was fifth fastest, with plenty of Dutch fans in attendance, and Australian team mate Daniel Ricciardo was sixth.
Monegasque rookie and Ferrari protege Charles Leclerc was an impressive seventh for Sauber while Force India, now under new ownership, saw Sergio Perez and Esteban Ocon lap eighth and 10th quickest.
Force India have had all their constructors' points taken away as a condition of their new mid-season entry but can expect to be ahead of Williams, now ninth but with only four points, before long.
Williams drivers Lance Stroll, son of Force India's new Canadian owner, and Russian Sergei Sirotkin were 17th and 18th fastest but ahead of the two McLarens.