Valtteri Bottas was in 'marathon man' mode on Wednesday, finishing fastest and clocking in with a massive 143 laps under his belt.
The Finn just tore relentlessly through Mercedes' tyre and aero data programme as the German squad sought to get on top of its recent degradation and balance struggles.
Bottas edged out Sebastian Vettel, at least in terms of lap times as the Ferrari driver racked in just 63 laps following a hydraulic leak in the morning and a data acquisition issue in the afternoon which limited the Scuderia's track time.
Toro Rosso's Carlos Sainz took over from Dany Kvyat and secured third fastest, but the happiest man in the paddock was undoubtedly Stoffel Vandoorne who was spared any drama and finally succeeded in putting his McLaren through its paces.
Team boss Eric Boullier even labeled the trouble-free session the best test day McLaren has enjoyed since the beginning of the year!
Renault's Sergey Sirotkin was another long distance runner on Wednesday, accumulating 123 laps and ending the day 9th fastest, just ahead of Sauber's Pascal Wehrlein and Force India's Sergio Perez.
GALLERY: All the action from the Day 2 in-season testing at Bahrain
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