Antonio Felix da Costa posted the fastest time in both Monaco E-Prix practice sessions, clocking in at 1m30.435s in FP2, while Nyck de Vries was fastest in FP1.
Following a red flag for Mahindra’s Alexander Sims, who pulled over at the entrance to the Rascasse with a damaged front-right steering arm, Da Costa posted his time in the final eight minutes of the second practice session.
Sims looked to have an incident with Sebastien Buemi of Nissan e.dams, which was investigated by the stewards but was not considered worthy of further penalty.
The Techeetah driver set the early pace with a 1m31.932s lap, but the Mercedes combination of de Vries and Vandoorne rapidly overtook him, with the former being the first driver to break into the 1m30s.
Following a brief yellow flag at the Swimming Pool section as Avalanche Andretti rookie Oliver Askew came to a halt, Robin Frijns took command at the summit, clocking a 1m30.678s despite a lock-up at the Nouvelle Chicane.
With only a tenth of a second between them, championship leader Jean-Eric Vergne moved into second.
It looked like Lucas di Grassi would overtake them both with a pair of quickest opening sectors before a Rascasse error thwarted his attempt to seize the lead.
Dan Ticktum next drew a yellow flag for a lock-up at the first turn, resulting in a dive into the Sainte Devote run-off, before Sims’ incident.
After the stalled Mahindra was cleared with eight minutes left on the clock, da Costa surged to the lead, with Mitch Evans closing in on him with a two-tenths gap.
Vergne then appeared to be on his way to making it a DS Techeetah 1-2 on the timing boards, but he smacked the wall on his way out of the Swimming Pool complex and had to go to the pitlane to check the damage right away.
At the end of the session, Evans attempted to overturn da Costa’s lead, but was held back by Pascal Wehrlein before going too deep into the Nouvelle Chicane, causing his lap to be ruined.
Frijns finished third, ahead of Vergne and Maximilian Guenther, on the basis of his earlier timesheet-topping lap.
De Vries finished sixth in FP2, ahead of Porsche teammates Wehrlein and Andre Lotterer, and Edoardo Mortara and Jake Dennis.
De Vries led the first practise session with a time of 1m31.154s, holding off a late assault from Nick Cassidy, who locked up at the Rascasse on his final lap before the chequered flag.
As a result, Cassidy finished second, 0.118 seconds slower than the Mercedes driver and just over three tenths faster than Edoardo Mortara. Da Costa finished fourth, ahead of Buemi and Lotterer, in that session.