World championship leader Kimi Antonelli topped the times for Mercedes ahead of defending champion Lando Norris of McLaren in Friday's second free practice ahead of this weekend's Belgian Grand Prix.
The 19-year-old Italian clocked a best lap time of one minute and 45.944 seconds to outpace Norris, who has a 10-place grid penalty for Sunday's race after taking a new battery, by 0.190 seconds with Max Verstappen third for Red Bull.
The four-time champion was 0.472 seconds adrift after a much-improved day using the team's traditional rear wing after ditching the much-criticised 'Macarena' wing, described by Verstappen as very dangerous.
He had crashed at both the Austrian and British Grands Prix, but bounced back to go fastest in the earlier opening session on Friday.
Seven-time champion Lewis Hamilton was fourth for Ferrari ahead of Isack Hadjar in the second Red Bull, Oscar Piastri in the second McLaren and Franco Colapinto who was seventh for Alpine.
This left George Russell down in eighth in the second Mercedes, more than 1.2 seconds behind Antonelli, ahead of Racing Bulls' rookie Arvid Lindblad and Liam Lawson, the pair pushing Charles Leclerc down to 11th in the second Ferrari.
The session ended after an extended red-flag interruption after Pierre Gasly crashed into the barriers in his Alpine. He was unhurt.
After a light shower between the sessions, the action began with Antonelli setting the pace in 1:46.911 with Verstappen chasing his time before a brief red flag delay to clear gravel from the track.
The Dutchman, showing some frustration, grumbled colourfully about his gearbox.
On resumption, several drivers swapped mediums for softs as Piastri joined the fray, after repairs for a hydraulics problem, in a spell of qualifying simulation laps.
Hadjar swiftly went top on softs before Verstappen and then Antonelli regained the initiative, the Italian clocking 1:45.944 to soar nearly five-tenths clear.
Ferrari responded with both drivers setting personal-best times in the first and second parts of the lap, but Hamilton wound up third behind Verstappen and ahead of Hadjar. He was 0.747 adrift of Antonelli.
Russell, 25 points behind his 'silver arrows' team-mate in the drivers' title race, tried a lap on softs, but was 1.285 seconds slower than the flying Italian as he settled for sixth.
Like Russell, Piastri was struggling to match his team-mate as Norris went second in 1:46.134, two-tenths off the pace. The Australian, last year's winner, went sixth, but was 0.982 adrift.
With 15 minutes remaining, the action was red-flagged when Gasly lost control of his Alpine and brushed the barriers at the Fagnes chicane. He was unhurt and walked away from his damaged car, which had lost its rear wing.
The action was suspended for 13 minutes allowing the teams only two minutes' action at the end of the session to complete their programme and engage in a few practice starts on the uphill grid.
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