DS Penske driver Vergne was considerably low on energy in the final stages of the 33-lap contest compared to Envision’s Cassidy, who kept the pressure up on him in a bid to take only his second career victory in FE.
But Vergne covered off the inside line into the Turn 3 hairpin - the primary overtaking point of the race - on every lap since a late safety car period triggered by McLaren’s Jake Hughes, preventing Cassidy from making a move.
Despite starting the final lap with just 2% useable energy remaining, Vergne was able to defy the odds to claim a first victory of the DS Penske partnership by just 0.400s.
Porsche’s Antonio Felix da Costa was elevated to the final spot of the podium in third after Sebastien Buemi was handed a late drive-through penalty for overusing the maximum power allowed.
At the start of the race, polesitter Mitch Evans led the field from Vergne, with Buemi slotting into third place.
But Evans would take an ill-timed attack mode early in the race on lap 7, which would drop him a net third behind Buemi and Vergne.
However, things would go from bad to worse for Jaguar just a few laps later, with Sam Bird crashing into the side of Evans and sending both cars out of the race on home turf for the squad’s owner Tata Group.
Bird was trying to pass the Nissan of Sacha Fenestraz for fourth place into the hairpin but ended up sliding into Evan’s car, pitching the Kiwi into a spin and with terminal damage into the car.
Both Fenestraz and Maximilian Guenther had nowhere to go and got caught out in the incident, although the two were able to continue without any damage.
The melee benefited a number of drivers, not least Cassidy, who now found himself third behind Buemi and Vergne.
Vergne wasted little time afterwards to pass Buemi for what would turn out to be the race-winning move, passing the Swiss driver going into the hairpin.
Buemi immediately armed the attack mode which was located on the outside of the same corner, which promoted Cassidy up to second and set-up a two-horse race for victory.
But before they could duel for the win, the safety car was deployed as Hughes crashed his McLaren and was left stranded on track.
At the restart, Rast went into the back of Dennis’ Andretti and immediately tumbled down the order with front wing damage, with Dennis also picking up a puncture on the incident and having to make an unscheduled pitstop for a fresh tyre.
It undid Dennis’ stunning recovery from 11th on the grid, with the Andretti driver having scythed his way to third, which would have been enough to take the championship lead from Pascal Wehrlein.
Instead, Wehrlein finished fourth behind teammate da Costa after an impressive drive of his own from 15th place at the end of the opening lap.
Sergio Sette Camara finished a strong fifth for NIO 333, while Oliver Rowland bagged a strong haul of points for Mahindra in sixth place.
Rowland even attempted an ambitious move over Buemi for third place on the outside of the hairpin in the closing stages of the race, but he ran wide and instead lost momentum that left him sixth at the finish.
Norman Nato scored his first points on the year in seventh, with Stoffel Vandoorne (DS Penske), Andre Lotterer and Edoardo Mortara (Maserati MSG) completing the points scorers.
