Following their crashes in Saturday's race, both Cassidy and Stoffel Vandoorne required extensive rebuilds on their respective cars, with Cassidy reporting that his steering was left-hand down at the start of the session.
After overnight rain, the Brooklyn circuit was damp, and as such there was a rapid rate of track improvement within the first 10 minutes of running.
Sergio Sette Camara headed the timing boards after the opening third of the session with a 1m11.167s, after failing to make the start of the previous day's race owing to his qualifying crash.
This was beaten by Mitch Evans, who got into the 1m10s before Antonio Felix da Costa beat that by a tenth.
Porsche's Pascal Wehrlein then picked up top spot before getting beaten by 0.001s by Jean-Eric Vergne, but the two were beaten into the 70s bracket by Sebastien Buemi - who logged a 1m09.960s.
Nyck de Vries then grabbed a 1m09.572s to go fastest, trailed by Mercedes team-mate Vandoorne, who set a time a quarter of a second slower.
The times continued to fall, and Vergne set a 1m09.294s - but was then just edged out by a resurgent Sette Camara, who posted a 1m09.288s to sit atop the timing boards with 10 minutes left.
Avalanche Andretti driver Jake Dennis then usurped the Dragon Penske racer and logged a 1m09.160s, but was soon displaced by Robin Frijns - who subsequently reported to his Envision team that the front brakes were running too hot.
Dennis returned the favour and logged a 1m09.008s, but Bird swooped on the fastest time and grabbed a 1m08.745s - which went unbeaten despite the late effort from Cassidy.
Lucas di Grassi, who was also caught up in Saturday's crash but required considerably less rebuild work to his Mercedes-powered Venturi machinery, placed third - 0.240s down on Bird's benchmark.
DS Techeetah's da Costa claimed fourth, ahead of Dennis, as Evans ended the session in sixth place.
Saturday podium finisher Frijns was seventh, ahead of Andre Lotterer and Oliver Rowland - who both set exactly the same lap of a 1m09.172s.
Wehrlein ended the session 10th ahead of Sette Camara, who was unable to keep pace with the ultimate frontrunners.
Result
| Cla | Driver | Team | Laps | Gap |
|---|---|---|---|---|
| 1 |  Sam Bird | Jaguar Racing | 20 | |
| 2 |  Nick Cassidy | Virgin Racing | 17 | 0.095 |
| 3 |  Lucas di Grassi |  Venturi | 15 | 0.240 |
| 4 |  Antonio Felix da Costa |  Techeetah | 19 | 0.247 |
| 5 | Jake Dennis |  Andretti Autosport | 20 | 0.263 |
| 6 | Mitch Evans | Jaguar Racing | 21 | 0.320 |
| 7 |  Robin Frijns | Virgin Racing | 17 | 0.409 |
| 8 |  Andre Lotterer | Porsche Team | 18 | 0.427 |
| 9 | Oliver Rowland |  Mahindra Racing | 21 | 0.427 |
| 10 | Pascal Wehrlein | Porsche Team | 19 | 0.467 |
| 11 | Sergio Sette Camara | Dragon Racing | 21 | 0.543 |
| 12 | Jean-Eric Vergne | Techeetah | 19 | 0.549 |
| 13 |  Stoffel Vandoorne | Mercedes | 16 | 0.589 |
| 14 |  Edoardo Mortara | Venturi | 13 | 0.783 |
| 15 | Nyck de Vries | Mercedes | 16 | 0.827 |
| 16 | Sébastien Buemi | DAMS | 20 | 0.963 |
| 17 | Oliver Askew | Andretti Autosport | 18 | 0.970 |
| 18 | Dan Ticktum | NIO Formula E Team | 19 | 1.090 |
| 19 | Oliver Turvey | NIO Formula E Team | 17 | 1.154 |
| 20 | Maximilian Gunther | DAMS | 19 | 1.388 |
| 21 |  Antonio Giovinazzi | Dragon Racing | 18 | 1.435 |
| 22 | Alexander Sims | Mahindra Racing | 19 | 1.450 |
| View full results | ||||
