Sebastian Vettel topped the times as he and Ferrari team-mate Kimi Raikkonen dominated Saturday's third and final free practice session for the Belgian Grand Prix.
The German four-time champion, who is 24 points behind defending champion Lewis Hamilton in this year's title race, clocked a best lap in 1min 42.661sec.
This put him 0.063sec clear of Raikkonen with fellow four-time champion Hamilton third for Mercedes, one-tenth adrift, ahead of his team-mate Valtteri Bottas, eight-tenths down. Bottas will start Sunday's race from the back of the grid after taking penalties for using a new engine.
Dutchman Max Verstappen, backed by thousands of his 'orange army' of fans who had made the short journey over the border, was fifth ahead of his Red Bull team-mate, Renault-bound Daniel Ricciardo.
Charles Leclerc was seventh for Sauber ahead of Sergio Perez in the leading Force India, Nico Hulkenberg of Renault and Esteban Ocon in the second Force India.
The session was extended by a late red-flag interruption when Belgian hope Stoffel Vandoorne spun after avoiding Bottas and brushed the barriers. He was unhurt.
On a cool morning of occasional light drizzle, the session began slowly before Raikkonen registered a serious quick lap to top the times in 1:43.425 for Ferrari.
Bottas responded with a fast lap, four-tenths off his compatriot's effort, for second and then Hamilton lapped within 0.098sec of Raikkonen's best to push his team-mate down to third.
With 20 minutes remaining, Bottas improved to go second before Vettel, finally finding his way, leapt to second as Raikkonen improved to 1:42.734. Hamilton trimmed his time to go third as the top three were separated by less than one-tenth of a second.
In conditions that may have favoured Mercedes -- a track temperature of 24 degrees Celsius and ambient air at 14 degrees -- Ferrari looked imperious as Vettel went top ahead of his team-mate with all four front-runners on super-soft tyres.
With just 10 minutes to go, the session was red-flagged when Vandoorne lost control after running wide on to the grass on the Kemmel Straight as he attempted to pass Bottas.
His car spun and ended up facing backwards on the inside of the circuit, only brushing the barriers. The Belgian driver, who seemed to be attempting to catch his McLaren team-mate to practice slip-streaming, was unhurt.
Vandoorne however was visibly angered by the incident and after a few expletives claimed the Mercedes "pushed me on to the grass."
The driver is under pressure to perform if he wishes to retain his seat next year.
"Ok, I didn't see him," responded Bottas, caught unaware as he remained on the racing line. After a six-minute pause, the session resumed with Red Bull-bound Frenchman Pierre Gasly promptly spinning his Toro Rosso car as he came out of the pits and ended without further incident.