George Russell says Friday's running at the United States Grand Prix had an element of the unexpected about it, with some drivers finishing higher up the order than expected.
Free Practice 2 in Austin was given over to testing Pirelli's development tyres, with teams allocated set amounts of fuel and unable to make set-up changes.
This placed extra emphasis on FP1, in which Russell finished seventh, almost a second shy of the pace-setting Carlos Sainz.
Lance Stroll and Fernando Alonso also ended the hour ahead of Russell in fourth and sixth respectively, and the Briton acknowledged the surprising nature of the FP1 rundown.
"FP1 was a bit of an odd session for everybody as well, where there were a few teams who were looking very fast, a little bit unexpectedly," Russell told media, including RacingNews365.com.
"Some other teams probably weren't as quick as we would have thought, and obviously having semi-missed FP2 because we were all running up own programmes, we don't really know what the pecking order is."
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Russell: The car is promising
Despite finishing below the likes of Stroll and Alonso in FP1, Russell said his Mercedes W13 appeared in good shape for the rest of the weekend.
"So far the car's feeling quite strong, which is promising," the Briton explained.
"I think you always get an inkling very early on in the day, if it's going to be a good weekend or a tough weekend.
"It's definitely not the worst that the car has been, but we don't know what Red Bull and Ferrari are going to do when they turn up tomorrow."
Mercedes are currently a solid third in the Constructors' Championship, and Russell added that he expected that form to continue for the rest of the weekend.
"I think we'll be okay. I think we should hopefully be in Q3 and fighting for those top six positions," he added.
"I'd like to think that we'll be ahead of the midfield cars this weekend, but I've learned in this sport to take nothing for granted."
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