Mercedes trackside engineering director Andrew Shovlin has described the team's 2023 F1 challenger as “a much calmer, more stable platform,” than its predecessor.
That saw the team scrambling to understand the faults with the W13 unless it unwittingly replicates them in 2023.
“We've had a solid start to testing,” he said.
“The car has run faultlessly from start to finish and that has allowed us to complete an ambitious programme for day one.
“It always takes a few days to understand a new car, but we've got a reasonable handle on where we want to improve the balance.
“It was encouraging that it's a much calmer, more stable platform to work with than the W13.”
The seven-time world champion managed the sixth fastest time overall with a 1:33.508s, while Russell set a best of 1:34.174s.
“The performance picture is always blurred after the first day so it's impossible to say where we stand, but we've already identified several key areas where we can find some performance,” noted Shovlin.
“We'll work on the assumption that we're playing catch up and need to pull out all the stops to find performance ahead of the first race here in one week's time.
“The next two days are going to be just as packed as today as we're squeezing every bit of learning we can into the programme.
“Hopefully the car continues to run like clockwork, and we can make the most of the remaining track time.”
Testing in Bahrain resumes at 10:00 local time on Friday,