George Russell and Lewis Hamilton fell three-tenths of a second short of Max Verstappen’s pole position lap for Red Bull but struggled on their last run in Q3.
Russell called his final lap “terrible”, while Hamilton had an engine oscillation problem that impacted his last effort as he reported feeling power drop outs.
Both Mercedes cars may benefit from getting a tow from Verstappen on the run from the starting grid to Turn 1, which is one of the longest of the season. Mercedes has typically performed better in race pace than through qualifying, but team principal Wolff was uneasy about expressing confidence it had the car to win on Sunday.
“I think in all my life, there’s only a handful of occasions that I’ve been confident, and never in Formula 1,” said Wolff. “So the truth is I don’t know.
“I’m annoyed about not being on pole, because it would have ticked a box, but equally having Max with his top speed advantage behind us would have been a problem tomorrow.
“Starting second and third can be advantageous, and I hope we can stick our nose or both noses into Turn 1 and disappear into the distance.
“But definitely that’s going to be difficult.”
Mercedes has three races left to avoid its first winless campaign since 2011, having struggled to match the pace of Red Bull and Ferrari through much of the season.
Asked if this was Mercedes’ best shot of winning a race so far this year, Wolff replied: “Yeah, I think so.
“The good thing is that in our simulations, we had [Mexico] in a way on the radar as being the best race. So that is good that it correlates, the virtual world correlates with the real world.
“The most important [thing] is that we really have the pace, and slowly but surely, we are going forward and learning the lessons for next year.”
One of the biggest boosts for Mercedes in Mexico came with the high-altitude conditions, leading to reduced levels of drag in the thin air, as well as allowing for high downforce packages to be used.
“For many years, Mexico wasn’t a good place for us because of the altitude,” said Wolff. “But [the] power unit guys have really given us a super strong engine here.
“We suffered less from our draggy car here, whilst running high downforce like all the others. Generally that has been better for us in the past.”