The Australian finished 10th in tricky mixed conditions last weekend, his second points-scoring result from six races.
His performance saw a significant pace improvement from practice to qualifying. He then recorded another confidence-building, composed performance.
Not for the first time this season, his progress caught the eye of team boss Andrea Stella, who described it as “remarkable”.
“The thing with the weekend was it was clean; gradually improved through the weekend; qualifying very, very close to Lando and then the race I think was probably the cleanest race we've had.
“All the other races we've had mechanical issues, damage in Saudi, food poisoning in Baku, all the red flags in Melbourne, so it was kind of the first – okay with the rain it wasn't that normal – but in terms of a result, and events during the race that happened to me, it was the most normal, which was nice to get some experience and just have a clean race.
“From that point of view, I think it was definitely a breakthrough.”
The turning point came as he was forced to push in qualifying, gaining confidence which in turn improved his lap time and improved his confidence even further.
“Obviously, qualifying is where it really counts,” he said.
“I think just getting comfortable with the car as well, I think the way we have to drive our car, you have to be quite confident with it.
“At a place like Monaco, it's quite tricky to build up that confidence, so I think in qualifying, I found some more confidence – a little bit with the way we set up the car and the track conditions but I found that confidence, and then it snowballed into more and more confidence.
“So I think it kind of just spiralled from there,” he added.
“I was getting a bit close to the walls, taking some more risk as well, so I think that's where it was just little bits everywhere.”
That boost in confidence was enough to see him breeze by Yuki Tsunoda into Sainte Devote a lap after his more experienced team-mate did the same thing.
For Piastri, it was also proof that he can deliver at that level; while he had the pace within him, he hadn't unleashed it.
Having now done that, his tail is up heading into this weekend's Spanish Grand Prix, opening practice for which begins at 13:30 local time (21:30 AEST).