Alexander Sims was fastest in the opening practice session in New York for BMW i Andretti Motorsport after a frantic 45 minutes.
Sebastien Buemi was second quickest for Nissan e.dams ahead of Envision Virgin Racing’s Robin Frijns and the championship leader, Jean-Eric Vergne for DS Techeetah.
Vergne's closest championship rival, Audi Sport Abt Schaeffler's Lucas di Grassi, finished the session in 12th place.
The session was notable for the number of lock-ups heading into Turn 6, with many drivers struggling for traction on their way into the corner.
Buemi, Andre Lotterer, Jose Maria Lopez, Daniel Abt, Antonio Felix da Costa, Sam Bird and Vergne - twice - were among the drivers who had locked up at that point of the circuit.
It is worth noting however that there is a change of track surface on the way in which makes the braking zone a bit trickier.
There was also what appeared to be a banana skin on the track between Turn 13 and Turn 14 although all the drivers were able to dodge it despite the Mario Kart references made in the commentary.
Behind the top four, Antonio Felix da Costa was fifth in the second of the BMW’s ahead of Jaguar’s Mitch Evans, with Edoardo Mortara seventh fastest for Venturi.
Andre Lotterer was eighth quickest in the second DS Techeetah entry ahead of Oliver Rowland for Nissan, and the top ten was rounded out by Stoffel Vandoorne for HWA.
Second free practice takes place at 10am local time.