The first of five public tests took place at the Leicestershire circuit in dry, bright conditions and saw all 10 teams and drivers use the full Donington Park circuit, modified to include an additional chicane at the exit to the Old Hairpin.
Thursday being the first outing for many of the drivers, the day focused on getting to grips with the Spark-Renault SRT_01E cars with German driver Daniel Abt, driving for Audi Sport Abt, laying down the early benchmark for the morning session.
Times began to tumble in the afternoon session with Buemi once again on the pace, posting a 1:35.475s with under an hour to go and holding on to the top spot until the end of the day.
Abt's Lucas di Grassi finished over a half a second shy of the Swiss despite only running during the afternoon session with Virgin Racing's Sam Bird a further three-tenths back in third.
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Mahindra Racing's Bruno Senna ran well all day to finish fourth with Venturi's new signing and ex-Le Mans driver Stephane Sarrazin rounding out the top-five during his first outing in a fully-electric single-seater.
The day also saw outings for several of the championship's new signings including Amlin Aguri duo Katherine Legge and Antonio Felix da Costa, Venturi's Nick Heidfeld, Trulli's Michela Cerruti and Dragon Racing's Mike Conway.
Former F1 racer Jerome d'Ambrosio and Spain's Antonio Garcia tested for China Racing with Scott Speed making his test debut for Andretti - sharing the car with IndyCar legend and Formula E ambassador Gil de Ferran.
Buemi said: "I'm more than happy to be honest. I didn't have any problems with the car at all and that meant we were able to learn quite a lot about it. It's always nice to be P1 so let's hope it continues tomorrow.