In a race with three mandatory tyre changes following Pirelli reliability concerns, drivers were able to push hard in each of their four stints rather than having to conserve their rubber for longer.
Behind Red Bull's sovereign winner Max Verstappen, Piastri clinched his second consecutive podium, picking up where he left off after winning Saturday's sprint in what he described as a gruelling race of 57 qualifying laps.
"Definitely the hardest race I've had in my life," Piastri said. "With the three stops, it was basically flat out, so it was 57 qualifying laps which I definitely feel like I've done.
"A really good race, happy that all tyres stayed together."
Piastri started from sixth after seeing his best qualifying lap deleted on Friday, but at the start he received a massive boost when Mercedes pair Lewis Hamilton and George Russell collided.
A spinning Russell hindered Fernando Alonso and Charles Leclerc, allowing the Australian to slip through into second on the inside.
Over the next 56 laps he again proved that that's where the McLarens deserved to be on merit. Team-mate Lando Norris, who had lost both his Q3 laps, underlined that point by moving up from 10th to third.
"Turn 1 was nice," Piastri smiled. "That was definitely in the game plan before the race! But yeah, really impressive pace."
Norris felt he "probably had the best pace out there" as he came through the field, having taken the lap 5 restart in sixth after the Mercedes fratricide.
"Just a mega race from start to finish," he added. "Good start, good pace throughout the whole thing, probably the best pace out there today, so I'm happy.
"Stressful, hot, sweaty, a little bit tired, but great job for the team, three [podiums] in a row now."
Norris agreed that the maximum tyre stints of 18 laps made the already physical race on the hot and high downforce Losail circuit even harder.
"Yeah, I think the three-stop made it a lot harder, just physically, you can push a lot more," he explained.
"Even the last stint you could pretty much push flat out so, probably one of the hardest races I've done in a way. But it's a nice challenge.
"And congrats to Oscar, no mistakes. And, of course, Max once again."
