The Belgian kept improving through his three-hour afternoon session to repeatedly retake the lead of the timing screens and end the penultimate day on top.
Vandoorne lapped the Circuit Ricardo Tormo in 1m26.045s to end the day fastest and he found a healthy nine-tenth margin over the Monday pace that was set by Robin Frijns.
Mortara’s switch to the higher power 250kW mode, up from the regular previous 235kW limit for attack mode, late in the day guided him to second – 0.044s adrift.
Although both the factory team and its Venturi Racing customer squad were quick to dismiss the turn of speed in testing conditions, in addition to the 1-2 in the free test session they also locked out the top four places in the Tuesday morning simulation race.
Jake Dennis, the rookie star of 2021 who marginally missed out on a shock debut title, bagged third for Andretti Autosport and was only 0.011s slower than Mortara.
With the locked-in homologation cycles regulating that teams must carry over the same powertrains as used in 2021, reliability issues were few and far between.
The only red flag came as a result of two-time champion Jean-Eric Vergne having a small spin and while he was able to continue, some marshals were sent out to clear up some gravel as a precaution.
Edoardo Mortara, Venturi Racing, Silver Arrow 02
Photo by: Sam Bagnall / Motorsport Images
Defending champion Nyck de Vries was fourth quickest and was among the front runners consistently.
Pascal Wehrlein headed up the Porsche testing fight in fifth ahead of Jaguar Racing driver Mitch Evans and new Venturi signing Lucas di Grassi.
Andre Lotterer, who stole an early march to lead the session with his 1m26.732s effort, eventually slipped down to 10th despite shaving three tenths of his earlier flying lap.
DS Techeetah’s champion Antonio Felix da Costa had run fastest in the truncated morning stint that also accommodated the simulation race.
However, he was slowest in the afternoon with his unrepresentative 1m30.488s lap.
But the Portuguese did complete the most tours of anyone with 52, eclipsing the next best of 47 set by his team-mate Vergne.
Vergne too was propping up the order in 20th, with the black-and-gold cars split only by Alice Powell.
The W Series racer subbed in for Frijns for the duration of the day, but he will return to the cockpit for the continuous final six-hour session on Thursday – after Wednesday’s dedicated media timetable.
Indy Lights champion and series newcomer Oliver Askew clocked 11th for Andretti Autosport with his fellow debutants Antonio Giovinazzi and Dan Ticktum snaring 17th and 19th respectively.
Giovinazzi’s performance was notable for a clocking a 15-minute penalty for exceeding track limits, with Ticktum and Dennis also gaining five-minute reprimands.