The Frenchman returned to winning ways with his first trip to the top step of the Formula E podium since Rome, Season 7, and he did it in some style. Vergne made his way to the front of the pack on Lap 15 - the double champion sweeping by Buemi at the hairpin after the Jaguars had removed one another from the equation two laps prior.
That moment saw Sam Bird make a lunge on the dirty side of the track on fourth-placed Sacha Fenestraz (Nissan). The Brit couldn't get his I-TYPE 6 stopped in time and collected teammate Mitch Evans, running third at the time - pitching the Kiwi's car into a spin and sending both into retirement and the unlucky Fenestraz tumbling down the order with them, in a race where a podium double - at the least - looked a possibility for Jaguar.
Vergne led the way from that moment but had his mirrors full of Cassidy's Envision Racing machine as the chequered flag drew closer. The New Zealander had managed to gather up an extra four percentage points of usable energy on Vergne come the closing stages of the race but the latter is the consummate Formula E fighter and used every trick in the book to keep him at bay and cross the line first - surely one of his best wins and one that will live long in the memory on Formula E's first visit to India in front of a sold-out crowd of over 25,000 people.
Buemi followed home in third but an overpower infringement saw him demoted to 15th spot via 17-second penalty, equivalent to a drive-through. That promoted Porsche's da Costa onto the podium in his 100th race - the Season 6 champion having started the race 13th. Teammate Pascal Wehrlein crossed the line fourth after picking his way through the order from 12th on the grid.
Sergio Sette Camara kept his nose clean and climbed through the pack to produce NIO 333's best result since Berlin, Season 4 - and all the way from 15th on the starting grid. Oliver Rowland, meanwhile, made a move for the podium on Buemi - not aware of the Swiss' impending penalty of the time - with just a lap to go. It didn't work out and saw him shuffled to sixth. Nevertheless, his first points of the season at Mahindra's home race. Norman Nato steered to seventh and the TAG Heuer Fastest Lap.
Reigning champion Stoffel Vandoorne (DS PENSKE) rounded in eighth for his best result of the season so far, while Andre Lotterer (Avalanche Andretti) and Edo Mortara (Maserati MSG Racing) rounded out the top 10.
Jake Dennis was the victim of an over-enthusiastic Rene Rast move on Lap 26 at the hairpin - the NEOM McLaren driver outbraking himself and rear-ending Dennis' Avalance Andretti. That proved costly for the Brit, who was running comfortably in fourth and on for a strong points haul - particularly given the strong finish for the other man out front in the standings, in Pascal Wehrlein.
That left Wehrlein with an extended 18-point advantage on Dennis, with Vergne leaping to third in the Drivers' standings. TAG Heuer Porsche has taken a 23-point lead over Avalanche Andretti in the Teams' World Championship.
Next up, Formula E's first trip to South Africa and Cape Town on 25 February for Round 5 of Season 9.
As it happened...
Evans launched well and made sure he countered Vergne and Buemi into the hairpin. The Jaguar driver held on and set about maximum energy saving; his engineer Josep Roca over the radio with the instruction.
On Lap 3, the battle for sixth saw Mortara get on the dust and fail to get his Maserati stopped in time - slipping into Cassidy's Envision Racing machine and well down the order to 17th, with front wing damage to boot. Come Lap 5, Evans led Vergne, Buemi, Fenestraz, Guenther, Cassidy, Bird, Rast, da Costa - up four spots - and Rowland.
At the hairpin on Lap 7, Buemi dived up the inside of Vergne and Evans - the latter having jumped early for two minutes of ATTACK MODE - for the race lead. Some move, and that Jaguar powertrain has been strong on both race pace and energy usage.
When Buemi took his first 50kW boost, he yielded the lead temporarily but managed to stay ahead of Evans' Jaguar - giving up track position early looked not to have paid dividends early on. Vergne followed through the ATTACK MODE loop on Lap 10 and also leapfrogged the Kiwi. First to third through the first round of ATTACK MODE activations and work to do for Evans.
Cassidy's progress continued on Lap 12 with a smart divebomb up the inside of Rene Rast's NEOM McLaren - not an easy feat on the fiesty German.
Lap 13 threw up an utter catastrophe for Jaguar TCS Racing. Bird spied an opportunity to make his way by Fenestraz for fourth spot but on the dirty line into the hairpin he couldn't get his I-TYPE 6 stopped and shunted his teammate into a spin - the pair both forced into retirement.
In the carnage that left Vergne, hounding Buemi for the lead and he swept by to put himself clear on Lap 15, once again at the hairpin. Through the second round of ATTACK MODE activations and that shunt, Cassidy and Dennis were the big beneficiaries from ninth and 11th to second and third come Lap 17.
Dennis wanted more than what was now fourth, having taken his second 50kW boost. Buemi had slipped by and the Brit wasn't having it - though he nearly made the same mistake as Bird; locking all four tyres to keep his Avalanche Andretti-run Porsche 99X Electric out of the back of Buemi's Envision Racing-run Jaguar.
Vergne had track position out front on Lap 20 but Cassidy wasn't far from the DS PENSKE's rear wing - and with two or three more percentage points of usable energy in-hand. Buemi in the sister Envision Racing sat third, a second or so back, with Dennis fourth and also a couple of percent up on energy on the leader. Rast had clambered from eighth to fifth, with Rowland tiptoeing through from 10th to sixth. Da Costa followed in seventh up from 13th at the start of the race with reigning champion Vandoorne next up having made up nine positions. Standings leader Wehrlein and Mahindra Racing's Lucas di Grassi rounded out the top 10.
On Lap 23, Hughes pushed a little too hard on the exit of the hairpin, lighting up his tyres and winding up in the wall - causing a Safety Car. The Brit said his mirror came loose and became jammed in his steering wheel - an odd shunt!
The restart followed three laps later and while Vergne led Cassidy and Buemi away, fifth-placed Rast immediately tripped over fourth-placed driver Dennis and took the pair of them out of contention - the German outbraking himself on the dirty line and climbing over the rear wing of the Andretti and puncturing the 99X Electric's right-rear tyre.
On Lap 29 of 32, Vergne had it all on to hold firm out front with the Envisions of Cassidy and Buemi right on his gearbox. It would need everything in the double champion's locker if he were to hold on for a memorable win, while trailing the pair on energy by three percent.
Rowland, meanwhile, had picked his way into fourth spot for Mahindra Racing on home soil though it wouldn't last. On Lap 30, the Yorkshireman tried to go around the outside of the hairpin to take third but got squeezed out by Buemi, allowing da Costa in the Porsche to pinch fourth.
With two laps, plus an added lap for time under the Safety Car, to come, Cassidy had enough energy to spare that he could fly flat out in pursuit of Vergne out front. There was nothing between the top three and the Envisions waited calmly - Cassidy some four percent up on energy.
Miraculously Vergne held on to win the inaugural Hyderabad E-Prix in stunning fashion, despite a massive deficit in energy - the DS PENSKE team engineering the victory to perfection from Cassidy and Buemi.