The 24-year-old Australian, without a win in four Formula 1 races since the Dutch Grand Prix in August, admitted he was concerned about both his qualifying and race pace.
"I think it is very important wherever you go to get qualifying right, and today I think race pace could have saved you – but I didn’t have that either," he said.
"So obviously, it's something I want to work on. Apart from Baku, this has been the first weekend where I have felt it has been a real letdown.
"It's been sub-par before, but I felt it was pretty good, so I've obviously got some things to try and understand from this weekend. It was clearly not all about qualifying.
"It was really difficult to get into a rhythm in any way."
Asked about the prospect of McLaren deciding to abandon their 'papaya rules' system of supporting both drivers equally and instead choosing to back one, he was against that decision.
"I don't know," said Piastri, who leads the drivers' standings on 346 points ahead of teammate Lando Norris on 332, with Red Bull's Max Verstappen snapping at their heels.
"I don't think so. We are so incredibly tight, and we both said we want an opportunity to try and fight for the championship because we deserve it.
"I think it is far too close to start picking one or the other."
Piastri has seen his once luxurious lead of more than 100 points ahead of rampant third-placed four-time champion Max Verstappen of Red Bull cut to just 40 after the Dutch driver's Texas triumph on Sunday.