On his first official Formula E outing following his return to the series after a year out, the Frenchman steered to a 1m25.776s lap, which was enough to pip next best driver Oliver Rowland in the Mahindra by a tenth of a second.
"It's good to be with everyone seeing some friends, some old mechanics as well that I've worked with," says Nato. In private testing, you're basically by yourself, fighting the lap time and finding some new improvement, but you don't really know where you are compared to the others.
"So it's a it's good to be setting times and basically trying to improve and see what your weaknesses are and what you have to do better the next day. So, that's what we're trying to do day by day and so far we we're making progress. It's good to end up the data as we did today - last night already was quite positive. We have one more more day tomorrow, which is going to be really important because it's the last one before Mexico."
Sebastien Buemi, Envision Racing's new signing, turned in a 1m26.066s to placve third with Edo Mortara continuing Maserati MSG Racing's hot streak with the fourth quickest time of the hour-long session.
The two Jaguar TCR Racing I-TYPE 6s, with Mitch Evans heading Sam Bird.
Reigning champion Stoffel Vandoorne (DS PENSKE) looked to have pinched the benchmark time at the last, only for his final run to be deleted for exceeding track limits.
Maximilian Guenther's streak of three table topping times came to an end - the German found himself 19th this time around and a couple of seconds away from the ultimate pace.
Testing comes to a close on Friday with two sessions, starting at 0900 local time. Follow it all live at fiaformulae.com/live.