In a brutal end to a wet qualifying on Friday in Las Vegas, Piastri's hopes of taking top spot were ended when Charles Leclerc went off in front of him and caused a yellow flag on the final lap.
Making matters worse, it came as Norris put in the fastest lap of the day in the other McLaren, putting him 0.323 seconds clear of Max Verstappen in second place.
Norris was tracking to finish ahead of Piastri anyway, but the yellow flag denied the Australian any chance of improving his time and qualifying higher than fifth.
"There were a few things as well at the start of the lap that didn't go great from an operational point of view," Piastri told Sky Sports.
"I had to mess around with a few things that didn't go how I wanted.
"I don't know how much time was in there, it's difficult to say. But what I can say is there was more out there that we didn't get to use."
Piastri had spent large parts of the final session of qualifying in the lead, before Norris found his best in the final few minutes.
The Australian had led the championship by as many as 34 points after the Dutch Grand Prix at the end of August, but has had one podium finish since then.
He will enter Saturday's race 24 points behind Norris in the championship, with a maximum of 83 points left through the final three events.
But if Norris is to finish ahead of Piastri in the Grand Prix, it means the Englishman can mathematically wrap up his maiden world championship in Qatar next week.
"We've got a good car underneath us, it seems to be working well in all kinds of conditions," Piastri said.
"I think we can have a strong race tomorrow and hopefully make up some spots."
Red Bull's Verstappen is the other man still in title contention, but his hopes of a fifth straight championship will be over if Norris wins and he finishes third or lower.
Norris' pole marked his fourth straight, while he has also won the last two grands prix to take control of the title race.
Carlos Sainz was third in the Williams and George Russell fourth in his Mercedes.
Liam Lawson will start sixth and Fernando Alonso seventh, with Leclerc eighth following his last-minute spin.
Seven-time world champion Lewis Hamilton was earlier one of the major victims of a treacherously wet and cold first session of qualifying, with his Ferrari 20th and last.
"Boy it was stressful as hell," Norris said.Â
"It was pretty nasty, probably some of the worst conditions, if not the worst. It was so slippery, so difficult."
