Lando Norris was fastest in Friday’s second hour of running, just over two-tenths clear of Piastri in second.
The Australian had sat out opening practice for Ryo Hirakawa who took his place as the team completed its mandatory rookie running.
Once in the car in Free Practice 2, Piastri was quickly up to speed and was left encouraged by what he found under him.
“I’m pretty positive,” he said of his session.
“I obviously just did FP2 and was pretty happy with the car straight away.
“The pace, I think we’re very happy with – hopefully, we can keep that pace into tomorrow.”
While McLaren topped the timesheets, Nico Hulkenberg was a surprise third-best for Haas.
The German was 0.462s off Norris’ pace and just over a tenth faster than Carlos Sainz in fourth.
However, neither Piastri nor Norris expect their advantage to remain, with suggestions both Ferrari and Mercedes will close in as qualifying approaches.
“I think the others will probably find a bit of a step, I would imagine,” Piastri reasoned.
“If we can get that kind of advantage, we’d be pretty happy.”
Norris suggested McLaren’s performance flattered a little with other teams not stressing their machinery to the same extent.
“Totally looks probably better than it is,” he claimed.
“I don’t think the others turned up their engines yet, so it might look glorious for now but I think we’re still going to have a tough fight tomorrow.”
McLaren holds a 21-point advantage over Ferrari in the constructors’ championship with only Sunday’s race remaining.
There is a maximum of 44 points on offer, meaning the Woking squad, which last won the constructors’ championship in 1998, can’t relax just yet.
However, the promising start has given the team confidence heading into the rest of the weekend.
“The pace today’s been very strong, so that can only give you confidence,” Piastri reasoned.
“Tomorrow’s obviously a very different day and I’m sure the others will find their feet a bit more,
“I think considering I only did one session, I’m happy with the day’s work.
“Hopefully we can continue that.”
Final practice is Abu Dhabi begins at 14:30 local time (20:30 AEDT) ahead of qualifying at 18:00 (midnight AEDT)