Contrary to Thursday's windy and wet conditions, Friday proved to be wonderful for testing, with ideal conditions greeting the teams as they headed into the final day of running before heading to Melbourne.
Kimi Raikkonen was the first man out on track today, soon followed by Russell for Williams and Grosjean for Haas.
Perez and Hamilton joined a minute later, and interestingly were spotted with smoke coming out of their Mercedes power units when accellerating out of Turn 5. Perez returned to the pits, but Hamilton continued for another lap, indicating it wasn't too much of a worry. 5 minutes later, another big puff was seen on Hamilton's W11 on the exit of Turn 11.
Meanwhile, Carlos Sainz was out to go fastest early in the morning. He went quickest on C4s with a 1m18.109s in the McLaren, and further improved that after a change to C2 tyres to 1m17.508s. The Spaniard seemed rather at ease with the McLaren MCL34, and improved again 20 minutes later, down to 1m17.255s.
Then, after switching to C3 tyres, he went another bit faster, raising the bar to 1m16.822s and at the time more than a second clear of second-placed Grosjean in the Haas VF-20.
Kimi Raikkonen on the other hand spun without much harm and was able to continue without help. Grosjean did the same in the haas a bit later.
Williams weren't at all worried about performance at that stage, as Latifi was seen running a new rear wing with his car equipped with numerous pitot tubes to verify that car's aerodynamic properties.
Halfway into the morning, Perez put Racing Point on top of the timesheet by lapping in 1m16.658s on C3s. That glory didn't last, as Leclerc got the better of him with a lap in 1m16.457s, despite being some 30km/h down in the speedtrap on Raikkonen in the Ferrari-powered Alfa Romeo.
As McLaren switched back to harder tyres and focused on longer runs, Leclerc improved even more on C5 tyres to 1m16.360s. Ricciardo initially jumped up into second on the same specification soft tyres, but on his second effort improved to 1m16.276s to take the top spot.
The final 30 minutes of the morning session didn't see anyone improve Ricciardo's time, making the Renault shine in the spotlights.
The afternoon session kicked off with the predictable spectacle, as most drivers entered a programma of race simulations, using those last four hours of testing to get the final bit of extra mileage into the car. With 2 and a half hours remaining, this means Leclerc was on top of the sheet with 128 laps, followed by Kvyat's 122 laps and Sainz with 109.
Ocon then set a number of personal bests but was unable to beat his team mate's time of the morning session.
As Leclerc continued the high mileage, counting 150 laps with 90 minutes left on the clock, Bottas went out for some faster runs, taking on the C5 Pirellis. Several improvements aligned, he ended up with a personal best of 1m16.196s.
He was nearly beaten by Verstappen a few minutes later, as the Dutchman managed 1m16.384s on the medium C3 compound tyres.
Bottas's best wasn't beaten anymore, but Mercedes's lack of very long runs today, along with the frequent puffs of smoke coming from the Mercedes engine were certainly a worry. Even though they appeared fastest in testing, there seems to be some head scratching for the Mercedes designers before they deliver their final Melbourne specification.