Lewis Hamilton admitted to a "difficult" opening day of work at the Hungaroring where Mercedes' W13 was left in the dust of its Ferrari and Red Bull rivals.
Hamilton and teammate George Russell were unable to get within less than 0.856s of either Carlos Sainz or Charles Leclerc, Ferrari's pacesetters on Friday.
Russell was P5 in the first practice but regressed to P8 in the second session that Hamilton concluded a lowly P11, the Briton clearly unsettled by his car's lack of consistency from one weekend to another.
"The car is a bit of a struggle," Hamilton said. "It's crazy how it swings so much from track to track. Just [keeping my] head up, trying to figure out how we can get the car working at the moment.
"It's a little bit loose and not doing what we want it to do. So yeah, difficult day."
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The performance was undeniably a setback for the Brackley squad which was expecting in light of its season-best performance last weekend at the Circuit Paul Ricard.
"Nothing has changed on the car since last week," Hamilton added. "I'm the same driver this week as I was last week. But for some reason, this track, it's not working as well.
"It's going to be a tough weekend, that's for sure, but we'll give it everything and see what we've got."
Mercedes trackside engineering director Andrew Shovlin revealed that the team had once again experimented with set-ups in a bid to improve its car's behavior and pace.
"We came in sort of wanting to do some experiments with the car and I think the ones that we did in FP2 with both [drivers] have taken us backwards," he said.
"The first session we looked a bit stronger, the car was more together. There’s a couple of things that I’m pretty certain we are going to be undoing overnight, because it didn’t look great."
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On the other side of the Silver Arrows garage, Russell felt that Mercedes' underperformance was mitigated by experimenting with set-ups.
"The conditions for Sunday are going to be drastically different, so we were trying quite a few things with the car, using it as a bit of a test session to be honest," Russell said.
"You can try and optimise a few things for today, but there's no use of that, it's all for the rest of the weekend.
"Even though it was a very tough day, I think it's been a productive one."
But Russell nevertheless acknowledged that the team was still "definitely a bit further away than we would have expected."
"But I think tomorrow is going to be a totally new day and Sunday will also be a very different day, so not all is lost yet," he concluded.
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