Sergio Perez posted the quickest time of the Bahrain test week so far as he topped the morning session at the Bahrain International Circuit on Saturday.
Perez worked his way down to a 1:33.105 on the Soft C4 tyre to finish almost a second clear of Alfa Romeo rookie Guanyu Zhou, who used the same rubber.
It came after Red Bull rolled out a significant upgrade package for the final test day, with the RB18 featuring revised - and more sculpted - sidepods, while there were also visible changes to the floor arrangement.
Perez's morning effort was some half a second up on the official Friday benchmark, a 1:33.532 posted by Ferrari's Carlos Sainz, before Kevin Magnussen clocked a 1:33.207 during Haas' prolonged session (permitted after freight delays).
While Perez topped the times, the most productive driver over the first four hours in terms of mileage completed was Pierre Gasly, who racked up 91 laps en route to the third-fastest time (C4).
Hamilton ninth out of the 10 runners
Mercedes' quiet start to the final day of testing continued as Lewis Hamilton wound up ninth out of the 10 drivers in action.
Hamilton's best time, set on the C5 tyre, was some three seconds off the pace, as he worked his way up to almost 80 laps in a bid to get on top of the porpoising issues that are giving the team a headache.
In the middle of the timesheets, Friday pace-setter Sainz put his Ferrari fourth on the C5 rubber, followed closely by Alpine's Fernando Alonso and McLaren's Lando Norris on C4s.
Norris was in action again, after teammate Daniel Ricciardo tested positive for COVID-19, with McLaren attempting to make up for lost time after flying in parts to rectify their early-test brake issues.
Nicholas Latifi (Williams) and Lance Stroll (Aston Martin) were the other drivers to slot ahead of Hamilton.
After a water pressure leak earlier in the morning, Magnussen's session was cut slightly short by a separate fuel system issue, as he brought up the rear – having started his day an hour early due to Haas' aforementioned concession.
You can stay up to date with all the action from Bahrain in the dedicated RacingNews365.com live blog.
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