Liam Lawson and Yuki Tsunoda were the slowest of the 20 runners in Free Practice 1, more than 3.5s off the pace.
A change in approach in Free Practice 2 netted improved results, with Tsunoda 10th fastest and Lawson 15th.
“Challenging, honestly,” the New Zealander said of his first day on the Las Vegas Strip circuit.
“It’s obviously extremely cold and the track, earlier, was really, like really slippery, really dirty, so obviously you’re just waiting for it to build up.
“Then P2 was a bit better, still obviously very cold, a lot colder, but the track’s getting better and obviously we’re learning things as well.
“We started the day really slow, to be honest and then we’ve made a step and learned quite a lot.
“We both went quite extreme in similar directions but in different ways and I think we learned quite a lot from it, so hopefully we can use that tomorrow.”
RB finds itself in a precarious position in the constructors’ championship after Alpine’s surprise double-podium at the Sao Paulo Grand Prix last time out.
That rocketed the Enstone team from ninth in the standings to sixth, five points clear of RB in eighth.
Alpine showed promising pace with Pierre Gasly on Thursday in Las Vegas, and both Haas drivers finished inside the top 10 at the end of Free Practice 2.
With only two races remaining beyond this weekend, dropping points now could have a decisive impact on the RB’s end-of-season result.
Lawson, however, suggests that, with the findings made on Thursday, his squad has the potential to be knocking on the door for championship points.
“I think for sure we have the knowledge, the points taken from today, to make a step tomorrow, but then everybody else is making steps as well,” the 22-year-old noted.
“I have no idea where in that we sit, but I’d like to think that obviously for myself I have a bit of a further step to make and hopefully we can be punching on the back end of the top 10.
“But it depends on how everyone else does as well.”
A final hour of practice remains ahead of qualifying in Vegas, which begins at 22:00 local time on Friday (17:00 AEDT Saturday).
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