Zhou tops the timesheets and Russell suffers a hydraulics failure as Max Verstappen enjoys final outing in RB19 before the season opener.
Though testing rarely sets the world alight - especially in locations like Bahrain where there is no chance of interference from the Weather Gods - today did have its moments.
OK, next weekend's result appears to be a foregone conclusion - of which more later - but in terms of the rest of the field it is still too early to start claiming who's hot and who's not.
The highlight of the day had to be this morning's close encounter of the wrong kind, when Carlos Sainz almost came to grief after a mix up during the practice red flag restart procedure, almost hit by Lewis Hamilton as he tried to make his way around Lando Norris' McLaren.
This afternoon, while the practice restart took place without any issues, just moments earlier, as the VSC system check got underway, Guanyu Zhou was stranded at the end of the pitlane whilst Logan Sargeant's Williams appeared to suffer a phantom hybrid issue. On the day that season 5 of Drive to Survive was launched, the 'fake' dramas seemed appropriate.
Anyway, back to Verstappen.
Having driven all day yesterday, this morning the Dutchman handed over to teammate Sergio Perez., who completed 76 laps without incident.
After the lunch break, whilst the majority of teams were still working on their cars, adapting them for the change of driver, Verstappen was already out on track and posting a time good enough to go third.
While other drivers began to head out Verstappen improved to second and then, inevitably, went quickest.
After 18 laps the Dutchman headed back to his garage, where the screens went up to in order to keep out prying eyes.
With Zak Brown having already warned that not too much should be expected of McLaren in the early races, as if to prove the point Oscar Piastri was out of his car and talking to his mechanics, there were few smiles.
There were even less smiles at Mercedes when George Russel ground to a halt with a hydraulics failure, causing the second red flag of the test.
"We've confirmed it was a hydraulic failure," Mercedes subsequently tweeted. "That's likely to be the end of our running for today." Indeed it was.
Fernando Alonso was one of three drivers doing 'a Verstappen', in the sense that they were at the wheel all day, the others being Zhou and Logan Sargeant.
Still unsure who his teammate will be next weekend, Alonso went second, repeating the order we witnessed yesterday. Even more impressive was that the fact this was the Spaniard's 116th lap.
Shortly after, albeit on the very softest rubber, de Vries went second.
At a time most were finally looking to up the pace, Leclerc opted for a short run on the hardest compound, while Zhou went for the softest in the range and swept to the top of the timesheets.
Yesterday, Verstappen completed 157 laps, while today Alonso completed 130, Zhou 133 and Sargeant a very impressive 154. Other than the obvious reliability, the fact that all three finished in the Top Seven suggests they also have pace.
While it was all smiles at Alfa Romeo at Alpine there was frustration as the team experienced what appears to be an issue with the rear axle that meant it took minutes - minutes!!! - to remove rear wheels on Ocon's car.
Then, as the VSC system check got underway, as if to add a little drama to the moment Zhou ground to a halt at the end of the pitlane, while Logan slowly climbed from the car as if it was ‘live'.
While this was initially assumed to be practice for the American rookie, as mechanics gathered around the car clearly not wanting to touch it, it was unclear if the car was indeed live. The car was subsequently pushed into its garage and cordoned off.
Once again we has a red flag restart practice and once the all-clear was given, de Vries headed out, followed by Hulkenberg, Piastri, Gasly, Leclerc and Verstappen.
Again they lined up on the grid, this time with de Vries on pole, and again the start was aborted and they headed off on another formation lap. Unlike this morning however there was no confusion, and de Vries led Hulkenberg towards Turn 1.
As we said, Verstappen and Red Bull look a comfortable bet, and while Ferrari looks to be second best, what of Mercedes and the rest?
Among those best suited to give an opinion, is Pat Symonds, formerly with Williams and Renault and now technical boss at F1 itself.
"I think what we are seeing here is what we are seeing a lot of in the new cars," he said of the RB19, while talking to Sky Sports, "we are not seeing the revolution, we saw that last year, what we are seeing now is the evolution.
"If you look at that car now you will not see many changes... the aerodynamicists have had to optimise and with the rule change on the ride height they lost performance and I think talking to people up and down the pit lane Red Bull have found that performance back again.
"A lot of work will have been going on to get the weight off and I think those are the things we are looking at this year. You've got these stringent safety tests that the chassis has to go through, little things like the roll hoop being smaller means you can save a little weight. Most of that losing weight won't be visible things. It's a small thing to do, it's also a very expensive thing to do, but it's a little performance.
"This is a time of day when you start setting some fast times," he continued. "That sort of things is not important to a team like Red Bull. Perez has done a very impressive race distance today headlining the fact that I think they are still the dominant team.
"Ferrari is an interesting concept," he added. "Because when you want to add performance to a car, a lot of it is about getting out of corners and using your performance on the straight. The interesting thing to me about the Ferrari, I still see this car porpoising quite badly. Where I see others looking quite better, they've still got the performance and yet the Ferrari is still bouncing... If you start pushing the limit again, of course you can get the car to porpoise again... There is a huge amount you can do on your simulators these days, but that final little bouncing it shows up in testing.
"That Mercedes, that is the car I have seen a massive difference in the ride compared to last year. It looks completely better. I think they are in for a much better season..."
The looks on the faces of Toto and his team as they reflected in the paddock at session end suggested otherwise, though the same could surely be said of McLaren, Alpine, AlphaTauri...
Like Verstappen, Zhou and Sargeant have had their final outings before next week's season opener, while, with Lance Stroll's fitness still in doubt, Felipe Drugovich is back in the Aston Martin tomorrow.
"Lap times in testing are of limited value," admitted Alfa Romeo, "but the team can take great encouragement by the good mileage racked up by Zhou Guanyu.
"We are well aware this is testing, of course, and everyone is trying different settings, but it feels nice to see my name and that of the team up there in the timing sheets," said the Chinese driver. "It's been a positive day overall, we got more mileage in and went through all the targets and tasks we had set for ourselves, so I can say I am happy.
"The car felt reasonably good, both in daytime and night-time conditions, and I felt more confident pushing as the day progressed. Today was the final day of pre-season testing for me, and I am very much looking forward to the start of the season next week. I feel ready and excited about the new campaign and I can't wait to be racing again."
"It was a good day for us with a lot of laps completed, said Alonso, "just what you need in a new car. We had a busy programme and tried a lot of different things.
"After a long winter it is good to get strong mileage under your belt early on and there is no better training than driving a Formula One car. I now feel fitter and sharper ahead of next week, which will be my first race with Aston Martin and I am very excited about that. I have another half day tomorrow so we will use this to continue learning and collecting as much data as possible. I am looking forward to getting back in the car tomorrow afternoon."
"We are pleased with the progress we have made during our second day," added team boss Mike Krack. "Fernando completed 130 laps, allowing us to run through our full test plan and gather further valuable data.
"We are continuing to get to know Fernando's driving style and what he wants from the car, but his feedback has been incredibly constructive and the changes we implemented overnight were received well.
"It is very difficult to make predictions on competitiveness based on a few days of testing because we have the full range of tyres available, different fuel levels and so many other variables to consider. We are just focussing on ourselves, preparing as much as we can, and getting through the job list.
"It will be next week after qualifying when we get a much clearer picture of how competitive we are. For our third and final testing day, we are pleased to have Felipe returning to the AMR23 during the morning session, with Fernando taking over in the afternoon."
Check out our Friday gallery from Bahrain, here.
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