The Finn put in a huge 139 laps in his Silver Arrow with a quickest lap of 1m 16.904s on supersofts, which was set in the morning session, putting him on top. Indeed, that pace was over six-tenths quicker than the P1 time Max Verstappen had set in the Red Bull on day one, but still behind team mate Lewis Hamilton's pole lap of 1m 16.173s for Sunday's Spanish Grand Prix.
It proved to be enough to keep Bottas 0.068s ahead of Ferrari’s Antonio Giovinazzi on the hypersoft compound, with the Italian behind the wheel of the SF71H one day after opening testing for Sauber. The Prancing Horse were certainly keen to get as much data as possible at the Circuit de Barcelona-Catalunya, and ran the most laps of any team with a mammoth 148.
The highly-rated Lando Norris did his glowing reputation no harm with a superb P3, the Briton leaving it late in the McLaren to set a 1m 18.039s. It was the third time the teenager has tested for the Woking outfit - after run outs in Hungary and Abu Dhabi last season - and one he’ll certainly remember.
Haas’s Kevin Magnussen made up the top four by going almost two-tenths quicker than Romain Grosjean’s time on the same hypersoft tyres on Tuesday. The Dane, however, saw his session ended after 75 laps when his American team made him park his car up on track as a precaution - an incident that brought the red flag out.
With rules stating that two of the four in-season test days must be given over to drivers with fewer than three Grand Prix starts, there were plenty of F1 hopefuls on show in Spain. One of them was Force India’s Nikita Mazepin, who finished fifth, while F2 star Jack Aitken - participating in his maiden test in a current car - was one place behind in the Renault.
Fresh from finishing tenth on Sunday, Charles Leclerc racked up 139 laps for Sauber – and his quickest put him in P7. Another driver familiar with this circuit, Robert Kubica, came eighth in the Williams less than a week after running in opening practice in Spain.
Toro Rosso decided to use two drivers on Wednesday with Sean Gelael behind the wheel in the morning before handing over to Pierre Gasly, who came ninth despite running just 39 laps.
Pirelli's tyre development programme schedule, which took place alongside this test, saw McLaren and Force India each provide a car. Stoffel Vandoorne was representing the former, and set the P10 time, while for the latter it was Nicholas Latifi.
British driver Jake Dennis also got his first taste of on-track F1 power, the Red Bull sim driver taking over duties from Verstappen and setting the 11th-quickest time.
So with testing now over for the teams and drivers, they'll turn their attention to the next round of the championship in Monaco.
* Running Pirelli test programme