The Australian became the first driver of the new season to retire from a race when he pulled up on lap 13 of 57 in Bahrain owing to a wiring loom issue that could not be solved by pitting for a new steering wheel.
Team-mate Lando Norris, meanwhile, had to pit six times to replenish the Mercedes-supplied engine pneumatic system, which developed a pressure leak. He eventually classified 17th, last of the runners.
Despite the unreliability, McLaren was quietly pleased by its pace, which might have put it in point-scoring contention, after heavily playing down pre-season expectations.
With Alpine driver Pierre Gasly recovering from last on the grid to ninth, some were quick to poke fun at Piastri for his heated Alpine exit last summer amid a contract dispute.
But the FIA F2 and F3 champion has hit back at those suggestions, saying that beyond pure car performance, he was attracted to McLaren because the team made him feel wanted.
Piastri, who moved after the Contract Recognition Board rule against his Alpine deal that would have likely sent him on loan to Williams, said: "For me, it was never really a decision of the two teams. It never really came down to that.
"For me, it was clear that I wanted to join McLaren with the amount of passion that they showed to having me in the team, which was a massive, massive factor in that.
"So, I don't really view it in that same light. But obviously I'm very focussed on where I am now and trying to help the team move forward and get back to where we want to be."
Piastri says that he remains convinced by the recovery plan laid out by McLaren, with a heavily upgraded B-spec car anticipated for the Azerbaijan Grand Prix, round four in late April.
He was also asked whether there was disappointment now that McLaren is less competitive than when he signed in August, as it was then battling Alpine for fourth in the constructors' championship.
Piastri replied: "We're obviously not where we want to be at the moment. We've been very open about that.
"We've got a good development plan in place to try and get ourselves back to where we should be, which is chasing the top three or four teams.
"To get on the same level as those top three or four teams is difficult. We'll see what these new developments that we've got in Baku bring for us.
"But obviously, it's going to be a step in what's a multi-step plan throughout the year."
