Lewis Hamilton set the pace in a Practice Two session twice stopped by red flags at the Bahrain GP, one for a big crash for Red Bull's Alex Albon and the other when a loose dog ran onto the circuit.
Hamilton completed a late qualifying simulation on the soft tyres to top the session in a best time of 1:28.971, three tenths quicker than Max Verstappen - although the Dutchman's best lap came earlier in the session on the slower medium tyres.
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But it was a session under the Bahrain floodlights to forget for Verstappen's team-mate, Albon.
Fighting to keep his seat at Red Bull for 2021, Albon lost control of his RB16 and slammed into the barriers when running wide at the final corner on just his fourth lap of the session.
The accident caused what Red Bull boss Christian Horner described as "significant" damage to the car ahead of repair work into the evening, with Albon sidelined from the remainder of the session.
"It was just one of them things. I should have pulled out of it really, I was surprised by the lack of grip, but it's just one of them things," said Albon, who was given the all-clear in a routine medical check-up "Quite a difficult, awkward angle those crashes. So not fun, but all good."
Sky F1's Damon Hill, 1996 world champion, said: "Everyone's done this... but Alex Albon does not need this right now. Although he's still got the rest of the weekend."
After the clean-up job for Albon's crash, the session resumed but was almost immediately stopped again when a dog was spotted running around the circuit.
It is the second time in as many races that a dog has entered the race track and, fortunately, it managed to escape back under a fence and out of the venue.
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When the session eventually resumed for real, Hamilton worked his way to the top of the order to complete a Friday double in his first appearance on a race weekend as a seven-time world champion.
Unusually, Verstappen had been unable to better his time on the medium tyres (1:29.318) when he completed his qualifying simulation on the softs earlier in the session.
Valtteri Bottas was third in the second Mercedes, Racing Point's Sergio Perez fourth and Daniel Ricciardo fifth for Renault.
With four teams - Racing Point, McLaren, Renault and Ferrari - fighting over third in the Constructors' Championship heading into the season's concluding three rounds, the head of the midfield looked competitive on Friday's evidence.
Pierre Gasly was sixth for AlphaTauri with Lando Norris seventh in the lead McLaren.
Drivers continued to test Pirelli's 2021 tyres in the second session - although several delivered downbeat assessments on the product after the session, with Hamilton particularly unimpressed.