Vergne’s 1m17.482s left him just 0.20s clear of McLaren’s Jake Hughes as Envision’s Sebastien Buemi was a further 0.081s behind in Saturday morning's session.
Buemi topped the order with a 1m19.123s after the opening 10 minutes and just prior to a red flag after the ERT of Sergio Sette Camara was unable to recover to the pits after stopping on track.
Once running resumed nearly 10 minutes later, and with the session extended by five minutes due to the delay, Buemi’s team-mate Robin Frijns hit the top with a 1m18.733s.
The Dutchman then lowered his personal best to a 1m17.908s, before he was beaten by Buemi and Cassidy.
Lap times continued to tumble inside the final 10 minutes with Vergne posting a 1m17.456s that stood as the best effort until it was removed for track limits, leaving Hughes fastest with a 1m17.502s.
Vergne then moved back to the top, nearly matching his previous disallowed lap, which proved to be the session’s fastest time as a second flag ended proceedings early.
This was after Cassidy went off at high speed on the approach to the final corner, the Kiwi having to take avoiding action as cars ahead slowed to prepare for a flying lap.
Cassidy’s Jaguar suffered right-front suspension damage which will put his participation in today’s qualifying, due to be held at 1020hrs local time, in doubt.
During the first practice session on Friday evening, DS Penske claimed a 1-2 with Vergne’s 1m17.546s leaving him nearly two tenths clear of team-mate Stoffel Vandoorne as Cassidy finished third.
Maserati MSG’s Jehan Daruvala claimed fourth but team-mate and Tokyo E-Prix winner Maximilian Guenther finished 21st after suffering a technical problem which meant the German stopped on track before returning to the pits.
Mitch Evans (Jaguar), Nico Muller (Abt), Buemi (Envision) and Sam Bird (McLaren) completed the top eight, with current championship leader Pascal Wehrlein ninth for Porsche.
Camara finished just behind and less than seven tenths off Vergne’s time, as eight different teams occupied places inside the top 10.