Mortara got loose into the first corner and looked down and out by the end of the first sector - de Vries going three-tenths faster off the bat.
But Mortara regrouped and reeled off two rapid final sectors, beating de Vries in both, but the Mercedes driver was only just able to absorb his rival's late charge and held pole by the merest of margins - albeit was left "disappointed" by his pole-winning lap.
De Vries had dispatched Mortara's teammate Lucas di Grassi in the semi-finals, the Brazilian elevated into the final four after confusion had reigned supreme in his quarter-final bout with Antonio Felix da Costa, with the DS Techeetah driver under investigation for impeding the Brazilian.
Da Costa had missed his pit-exit signal and instead left on di Grassi's - leaving the Venturi driver initially stranded in the pitlane on a red light.
Mortara had made his way through to the final after seeing off Andre Lotterer and Robin Frijns, while de Vries had overcome Jean-Eric Vergne in the quarter-finals as DS Techeetah managed to get both cars among the duel stages.
Frijns' time in the semi-finals proved stronger than di Grassi's, earning him third on the grid.
Rowland and Frijns were drawn together in the third quarter-final duel - resuming their battle after both came to blows in the opening Diriyah race.
Frijns was able to find fractionally more speed than Rowland in each sector, nailing the final corner to knock the Mahindra driver out of qualifying. Rowland starts 10th after Friday's skirmish with Frijns earned him a three-place grid penalty.
De Vries had set the pace in the opening collection of runs in Group A, being the first driver to get within the 1m08s in the session ahead of the nominal mid-session lull.
Oliver Askew then got within a tenth of the race 1 winner, ahead of a flurry of purple laptimes that precipitated a battle over the top four spots in the session.
Sergio Sette Camara then charged to the top, but was quickly toppled by Jake Dennis and Pascal Wehrlein - before Andre Lotterer put them to the sword with a 1m08.224s.
Oliver Rowland then picked up the pace with a tenth over Lotterer, before de Vries returned to the top with a 1m07.939s. Di Grassi slotted into second, dumping Dennis out at the group stages.
Dennis starts eighth, elevated up a position after Rowland's penalty.
Nick Cassidy did not run in qualifying following his earlier crash in practice, which resigned him to the back of the opening session after requiring multiple repairs.
Da Costa took Stoffel Vandoorne off the top of Group B after the initial set of runs, although Edoardo Mortara posted a 1m07.724s benchmark while the track was marginally more clear after getting baulked on his opening run.
Da Costa got within a tenth of Mortara as Vergne also nipped ahead of Vandoorne, ahead of a final push from each driver in the session.
Vergne cemented his spot with a 1m07.968s lap, while Vandoorne failed to improve on his final run and was displaced from the top four - allowing Alexander Sims a brief sniff of a spot in the duels before Robin Frijns dumped the Mahindra driver out.
Mortara's benchmark remained unbeaten, while da Costa aborted his final lap having already been assured of a place in the knock-out stages.
Sam Bird tapped the wall half-way through the session, causing damage to his rear suspension which put a pin in his session - leaving him last overall in his group.
Diriyah E-Prix - Qualifying results:
| Cla | # | Driver | Team | Time | Gap |
|---|---|---|---|---|---|
| 1 | 17 |  Nyck de Vries |  Mercedes | ||
| 2 | 48 |  Edoardo Mortara |  Venturi | ||
| 3 | 4 | Robin Frijns |  Virgin Racing | ||
| 4 | 11 |  Lucas di Grassi | Venturi | ||
| 5 | 36 | Andre Lotterer | Porsche Team | ||
| 6 | 25 |  Jean-Eric Vergne |  Techeetah | ||
| 7 | 13 |  Antonio Felix da Costa | Techeetah | ||
| 8 | 27 | Jake Dennis |  Andretti Autosport | ||
| 9 | 29 | Alexander Sims |  Mahindra Racing | ||
| 10 | 30 | Oliver Rowland | Mahindra Racing | ||
| 11 | 94 | Pascal Wehrlein | Porsche Team | ||
| 12 | 5 |  Stoffel Vandoorne | Mercedes | ||
| 13 | 7 | Sergio Sette Camara | Dragon Racing | ||
| 14 | 22 | Maximilian Gunther | DAMS | ||
| 15 | 28 | Oliver Askew | Andretti Autosport | ||
| 16 | 9 |  Mitch Evans | Jaguar Racing | ||
| 17 | 23 | Sébastien Buemi | DAMS | ||
| 18 | 33 | Dan Ticktum | NIO Formula E Team | ||
| 19 | 3 | Oliver Turvey | NIO Formula E Team | ||
| 20 | 99 |  Antonio Giovinazzi | Dragon Racing | ||
| 21 | 10 | Sam Bird | Jaguar Racing | ||
| 22 | 37 | Nick Cassidy | Virgin Racing | ||
| View full results | |||||
