The McLaren driver will start fifth for tonight’s race with a best time four-tenth shy of pole-sitting team-mate Lando Norris.
Piastri had been half a step behind Norris throughout practice, the Brit topping the second and third practice sessions having been within a tenth of Charles Leclerc in Free Practice 1.
It left the 23-year-old looking for more from his car heading into Saturday before it all came together in qualifying.
“I think through practice it was a big struggle to be honest. I just had no pace,” Piastri said.
“Through qualifying I felt quite comfortable, was feeling much better with the car and in Q2 was strong, even Q3, just both my laps were terrible.
“The last one was looking good and a little bit quicker than what I’d managed in Q2, which would have put me well in the fight for pole.
“But yeah I just had a bit of a moment towards the end of the lap and, with these tyres this weekend, you have one little moment and it destroys your lap.”
That moment came exiting Turn 14, when Piastri lit up the rears as he accelerated out of the right-hander entering the long run towards the final complex.
With the rears overheated, negotiating the chicane at Turn 16/17 almost left the Australian in the wall, costing him further time.
The outcome was a comparatively slow lap, fifth position, and a frustrated Piastri critical of the Pirelli rubber.
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“It’s always tough to manage the tyres over one lap, which is frustrating,” he admitted.
“This weekend has been another step on top of that, I would say.
“One of my laps in Q1, Q2, you have one small moment early in lap and the rest of the lap is a disaster.
“Even if you have it at the end of the lap it still turns into a disaster.
“It’s difficult, it’s sometimes frustrating that in qualifying, we can’t really push everything to the limit because if you overstep it, you try and take one step forwards and three steps back.
“It’s not like it’s something new and something different for me compared to everyone else.
“It’s the same for everyone, and just haven’t done a good enough job today of respecting the tyres.”
While the McLaren is clearly rapid in Singapore, overtaking is notoriously difficult.
Even with the addition of a fourth DRS zone this year, which drivers hope will spice up the race, passing the Mercedes of George Russell and Lewis Hamilton is not a given.
“We’ll try our best. The race pace should be good,” Piastri said of his race prospects.
“Just not the easiest track in the world to overtake, so we’ll see what we can do.
“Not quite as many big braking zones as Baku to work some magic.”
While Piastri starts fifth, countryman Daniel Ricciardo will line up 16th after he was knocked out of qualifying in Q1.