George Russell was left pleased following his first experience with the W15 car in Bahrain, asserting it's a “good foundation” for the year ahead.
Russell set 121 laps during the day and was one of only two drivers (along with Max Verstappen) not to hand the car over to his teammate for the afternoon session.
Mercedes enters the new campaign hoping to improve on a difficult two seasons during which it has failed to contend for regular race wins.
Russell will sit out driving duties on Thursday as Lewis Hamilton jumps into the role, but was content with his maiden encounter with his new car.
“It was great to drive the W15 for the first time in anger today,” Russell said. “From hitting the ground, it felt like we had a good foundation to start from.
"We completed lots of laps and have plenty of data to go through tonight. We ended the day in a reasonably good spot, and we can build from here over the next two days.
"We will be focused on maximising mileage for learning rather than chasing an optimum sweet spot with the car.”
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W15 car 'nicer to drive'
Despite last season marking Mercedes' first winless campaign since 2011, it managed to pip Ferrari to the runners-up spot in the Constructors' Championship.
Russell concluded that the W15 is more pleasing to drive than last year's car having had eight hours of session time to assess the new Mercedes challenger.
“Overall, the W15 does feel nicer to drive than last year's car,” he said.
"We know that it's not about the feeling, but the speed. Nevertheless, today was about learning and not about chasing performance.
"We're focused on ourselves at this test, and it will only be next week where we see where we stack up against the others.
"It was a positive first day and I'm looking forward to being back in the car on Friday."
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