Max Verstappen finished top of the timesheet, as Red Bull enjoyed the perfect start to pre-season testing in Bahrain.

Despite deteriorating conditions as a sandstorm engulfed the Sakhir circuit, the Dutchman improved on his morning time in the afternoon, setting a 1m30.674s on the medium compound tyres.

As one of only three drivers to run all day, Verstappen also topped the lap count with an impressive 139 laps, 10 more than anyone else.

McLaren also continued their strong first day as Lando Norris moved up to second under the lights late on, just two-tenths behind the Red Bull on the same rubber.

Esteban Ocon was another driver to complete the full eight hours of running in third for Alpine, four-tenths off Verstappen's early benchmark.

Perhaps the biggest story of the day though was trouble at Mercedes, as Lewis Hamilton only clocked 42 laps in the afternoon in addition to six for teammate Valtteri Bottas in the morning.

While track conditions were of course very tricky, the world champion also appeared to struggle more than most in the W12 with several trips in the run-off areas.

And right at the end, there were more questions over reliability, as mechanics were seen donning their yellow gloves to receive his car in the pit-box which usually signals an electric issue.

Elsewhere, Aston Martin had a solid day with Lance Stroll capitalising on the better track conditions to take fourth, two seconds clear of teammate Sebastian Vettel.

Despite causing a red flag in the morning, Ferrari too will have few complaints with Carlos Sainz fifth.

One team that snook under the radar on Friday was Alfa Romeo, with Antonio Giovinazzi sixth just 0.026s behind the works Ferrari.

Daniel Ricciardo's morning best remained good enough for seventh as Yuki Tsunoda ended just half a second behind AlphaTauri teammate Pierre Gasly in ninth despite only using the hard compound tyres.

Hamilton's best time was only good enough for 10th in the Mercedes, a considerable 2.2 seconds off Verstappen's pace.

Down the field, Roy Nissany, the only non-race driver to be running this week, managed 83 laps for Williams in 14th.

Nikita Mazepin had a few spins en route to 15th in the slippery conditions. But the rookie did manage a strong 70 laps as he made up for the gearbox problems Haas and Mick Schumacher had suffered in the morning.

Full results from Friday can be seen below: