Charles Leclerc capped an impressive return to F1 action for Ferrari by heading their second successive one-two in Practice Two at the Belgian GP.
Leclerc took over from P1 pacesetter Sebastian Vettel in the afternoon's running at Spa-Francorchamps and his best lap of 1:44.123s was a full 0.6s faster than his team-mate's alone.
Mercedes, third with Valtteri Bottas and fourth with Lewis Hamilton, finished 0.8s adrift over F1's longest lap, with Red Bull more than one second off the pace.
"Today the Ferraris are the absolute benchmark and could be on Sunday - and also in Monza," said Toto Wolff, Mercedes' team principal, to Sky Sports.
Sergio Perez was an impressive fifth for Mercedes-powered Racing Point, although he ran into late trouble when the back of his car caught fire and he had to pull off the track.
Alex Albon finished 10th at the end of his first day for Red Bull but within 0.4s of Verstappen, with the Anglo-Thai driver's focus more on race set-up with his career at the team to start with a hefty grid penalty for engine changes on Sunday.
Verstappen, who does not have Honda's latest engine here, told Sky F1 he was running with reduced power during Friday as the team preserve engine mileage.
Title not wrapped up yet - Hamilton
Lewis Hamilton insists he can still lose the World Championship despite taking an almost unassailable lead into the second half of the season.
As Formula One roars back into life following the sport's summer shutdown, Hamilton is 62 points clear of Mercedes team-mate Valtteri Bottas with nine rounds remaining.
Hamilton headed on his break riding the wave of a fine performance in Hungary, passing Red Bull's Max Verstappen in the final laps to win for an eighth time from 12 starts this year.
The 34-year-old has never enjoyed a better start to a Formula One campaign - and usually saves his best drives for the business end of the year.
And with Verstappen - Hamilton's closest non-Mercedes challenger 69 points behind - admitting his hopes of catching his rival are improbable, it is little wonder that the Briton is expected to gallop to his sixth championship with rounds to spare.
"I take it as a compliment that people expect me to win the title," said Hamilton.
"But it doesn't make any difference to me.
"I know how much work I still have to do. If I don't turn up this weekend in Spa, or next weekend in Monza, or if I make mistakes, I can easily lose this championship.
"There are points available to turn the tables, so I will stay focused as I have done in the past. There are still races to win, areas that I want to improve on and areas that I don't want to drop. I truly believe I can do that."
Hamilton's return to action started on the back foot in Spa-Francorchamps. A throttle pedal failure restricted his participation in first practice on Friday, before he finished a distant fourth in the day's final running, nine tenths of a second off the pace as Ferrari dominated.
"That sounds dreadful," added Hamilton. "It was not a great start in practice one. We had a problem with the throttle and lost power. We went back out and had another problem so it was a bit of a mess.
"The car felt better later, but we still have work to do. The Ferraris look quick.
"We will keep chipping away, but we are in the mix."
Our F1 Insider fancies Sebastian Vettel for glory when Formula 1 heads to Belgium this weekend. Click the image below to have a read...