The Australian finished seventh, one spot up from his starting position after a largely anonymous race.
Piastri had expected a tough day in the office during Saturday night’s race, but confessed he wasn’t expecting it to be quite as difficult as it proved to be.
“Qualifying, we’ve got some ideas why it didn’t really come to us in Q3 but the race, I think, was more difficult than we expected,” he admitted.
“Especially on my side, it was a much, much more difficult race with the tyres than I expected going in.
“I mean, we knew it would be tough with graining, but the graining was a lot, lot worse than I feared.
“That part was quite unexpected, so I think we need to understand why it was.”
Piastri’s race was helped by a seemingly harsh penalty for a start infringement.
Officials deemed the 23-year-old had lined up out of position, though his McLaren appeared within the painted lines and did not jump the start.
“I didn’t feel like I did anything different or overshot it, but I mean, clearly I must have been a bit out,” he reasoned.
“It made a little bit of an impact at the start with after the first pit stop, but that was nowhere near the biggest problem I had tonight.”
Neither Piastri nor team-mate Lando Norris had pace in the race to challenge the front.
Piastri was 51.3 seconds back from race winner George Russell, a deficit that equates to more than a second per lap.
Norris finished only one place higher in sixth, a result that extinguished his title ambitions as Max Verstappen finished fifth.
That Russell won from his Mercedes team-mate Lewis Hamilton was something of a saving grace as McLaren battles Ferrari for the constructors’ championship.
Following the Vegas event, just 24 points separates the two teams.
McLaren must grow its advantage to 45 points following next weekend’s Qatar Grand Prix to guarantee itself the constructors’ championship, else that battle will go to the wire in Abu Dhabi.
“We’ve not won a constructors’ championship for over 25 years, so it would mean a lot,” Piastri said.
“For myself, it’s definitely a cool thing to be able to help the team achieve, if that’s what we do.
“Of course, we want to be a bit higher up in the driver standings too, but obviously not that much to play for in that championship now, so the full focus is on the constructors.”
The Qatar Grand Prix begins on Friday with opening practice at 16:30 local time (00:30 AEDT).
