Petronas SRT Yamaha rider Quartararo had fired in a 1m59.225s late on with a fresh soft rear tyre, smashing the existing Silverstone MotoGP lap record by more than seven tenths.
But he swiftly had his lap time disallowed due to a track limits infringement at Chapel, and an error at Brooklands on his final attempt meant he had been consigned to the 11th in the classification.
Marc Marquez’s 1m59.476s effort therefore stood as the afternoon benchmark at the checkered flag instead, the reigning champion having recovered from a low-side crash at Vale just over 10 minutes in the session.
But the stewards later reviewed track limits decision that had been made regarding laps by Quartararo, Rossi and Takaaki Nakagami and reinstated all three.
That meant Quartararo completed a clean sweep of Friday’s two practice sessions, ending up a quarter of a second clear of Marquez.
Maverick Vinales was another three tenths down in third, while Rossi moved up from 17th to fourth with his disallowed lap now able to be counted.
Cal Crutchlow and 2017 Silverstone winner Andrea Dovizioso completed the revised top six, while Nakagami moved up to 11th.
Revised practice two times
|1||Fabio Quartararo||Petronas Yamaha||1m59.225s||–||16|
|5||Cal Crutchlow||LCR Honda||1m59.993s||0.768s||16|
|7||Franco Morbidelli||Petronas Yamaha||2m00.183s||0.958s||18|
|8th||Miguel Oliveira||Tech3 KTM||2m00.360s||1.135s||16|
|9||Jack Miller||Pramac Ducati||2m00.392s||1.167s||14|
|11||Takaaki Nakagami||LCR Honda||2m00.492s||1.267s||16|
|16||Francesco Bagnaia||Pramac Ducati||2m00.788s||1.563s||16|
|19||Hafizh Syahrin||Tech3 KTM||2m02.417s||3.192s||16|
|20||Tito Rabat||Avintia Ducati||2m02.473s||3.248s||18|
|22||Karel Abraham||Avintia Ducati||2m02.993s||3,768s||14|