Championship leader Oscar Piastri was at a loss to explain his gap to McLaren teammate Lando Norris during qualifying for the Mexican Grand Prix, describing his recent loss of performance as "a mystery."
Piastri leads Norris by 14 points at the top of the championship, but has seen his advantage whittled away by Norris and Red Bull's Max Verstappen at the last four rounds.
After struggling to match Norris at last weekend's U.S. Grand Prix -- he qualified eighth on Saturday in Mexico -- 0.588 seconds off his teammate's pole position lap time.
Piastri will start from seventh on the grid due to Carlos Sainz's five-place grid penalty for a collision with Kimi Antonelli at last weekend's U.S. Grand Prix.
Piastri was unable to pinpoint the reason for his sudden decline in performance relative to Norris.
"I mean difficult to know, everything feels normal, but the gap was big in that session, it's been big all weekend," he said. "There's been some things where I feel like I can tidy it up and make some easy progress but not all of it, and I think in qualifying I did a reasonable job and the car felt reasonable as well, the lack of lap time is a bit of a mystery."
If Norris and Piastri finish where they start in Sunday's Mexican Grand Prix, Norris will take the lead of the championship by five points with four race weekends left to run.
Asked where his head was at after his second consecutive lackluster qualifying, Piastri said: "Ultimately just a bit frustrated with how the session's gone. You know, there's a lot of things I could worry about but ultimately being that far off when you feel like you've done a reasonable job is a difficult place to be and so that's my biggest concern at the moment."
Piastri's championship lead, which stood at 34 points just four races ago, was built on consistent performances through the early stages of the season.
The Australian said a large part of his frustration came from a feeling that his performance behind the wheel was no longer being reflected by his lap times on track.
"I've not changed really how I'm driving since the start of the season -- even compared to a few races ago when things were going really well," he said. "So it's difficult to pinpoint where the lap time has been lacking this weekend, but I'm sure we'll find it."