Envision Virgin driver Robin Frijns set the pace in practice for the second Diriyah E-Prix, beating the in-form Nyck de Vries with a last-gasp effort on Saturday afternoon.
Having dominated the first Riyadh race on Friday, Mercedes de Vries looked set to continue his unbeaten run in the 45-minute practice session, having broken his own lap record from qualifying and then sett a blistering lap of 1m07.440s on his full power run.
But Frijns, who failed to take part in qualifying on Friday after requiring a change of battery, managed to lap the circuit in 1m07.294s in the dying minutes of the session, outpacing his Mercedes rival by 0.146s.
Frijns' rookie teammate Nick Cassidy also made a late lunge up the order, his effort of 1m07.449s putting him third ahead of Oliver Rowland, who was the first driver to break into the 1m07s in practice using last season's Nissan powertrain.
Reigning champion Antonio Felix da Costa (DS Techeetah) ended up just over two tenths off the pace in fifth, recovering from a horrific performance in the first of the Diriyah races that left him well outside the points.
Edoardo Mortara was a promising sixth after scoring a podium for Mercedes' customer Venturi on Friday, ahead of the works car of Stoffel Vandoorne.
The Swiss driver then ended up crashing heavily in the barriers after practice had ended, going straight on at the chicane after completing a practice start.
Mortara has been taken away in an ambulance as a precautionary measure - but is conscious and talking.
Sebastien Buemi was eighth in the second of the two Nissans, ahead of the Jaguar of Sam Bird and the factory Audi of Lucas di Grassi.
The BMWs of Jake Dennis and Maximilian Gunther finished 12th and 17th respectively, the latter ending up more than a second off the pace, while two-time champion Jean-Eric Vergne could only finish 14th in the second DS Techeetah.
The only red flag of the session was caused by Andre Lotterer, who hit the wall at Turn 11 before coming to a rest at the following corner with visible damage to his Porsche.
Porsche now faces a race against time to repair his 99X Electric car in time for qualifying.
Lotterer's teammate Pascal Wehrlein, who qualified on the front row on Friday, was 18th quickest.
Diriyah E-Prix Saturday practice results
|1||Robin Frijns||Envision Virgin Racing||1m07.294s|
|2||Nyck de Vries||Mercedes||0.146s|
|3||Nick Cassidy||Envision Virgin Racing||0.155s|
|4||Oliver Rowland||Nissan e.dams||0.158s|
|5||Antonio Felix da Costa||DS Techeetah||0.218s|
|6||Edoardo Mortara||Venturi Racing||0.254s|
|8||Sebastien Buemi||Nissan e.dams||0.455s|
|9||Sam Bird||Jaguar Racing||0.484s|
|10||Lucas di Grassi||Audi||0.590s|
|11||Oliver Turvey||NIO 333||0.723s|
|12||Jake Dennis||BMW Andretti||0.733s|
|14||Jean-Eric Vergne||DS Techeetah||0.897s|
|15||Tom Blomqvist||NIO 333||0.956s|
|16||Norman Nato||Venturi Racing||0.962s|
|17||Maximilian Guenther||BMW Andretti||1.024s|
|19||Alex Lynn||Mahindra Racing||1.236s|
|20||Nico Muller||Dragon Penske Autosport||1.309s|
|21||Mitch Evans||Jaguar Racing||1.359s|
|22||Alexander Sims||Mahindra Racing||1.549s|
|23||Sergio Sette Camara||Dragon Penske Autosport||1.552s|