Lewis Hamilton has conceded it is a "shock" for Mercedes to have topped the timesheets on the first day of the Bahrain Grand Prix but insisted the new W15 "feels like a race car".
The seven-time World Champion led a Mercedes one-two in the more representative FP2 session to set up a pole position charge in the first qualifying session of the season.
It is a positive start for the Silver Arrows having struggled through the first two years of the current regulatory period, yet Hamilton is remaining grounded.
"This has been a crazy [Thursday], I was late this morning," said Hamilton.
"FP1, we were surprised, it was very windy this morning so it was a pretty difficult session for everyone, the track was so different compared to testing last week.
"Otherwise, it was feeling ok but we didn't really know where we stood.
"But we made some improvements over the session, I don't understand... it is a shock to see us where we are but we will take it for now.
"We can't get ahead of ourselves, we need to keep our heads down, keep working on the set-up and trying to extract more.
"Our long-run pace is nowhere near the Red Bulls so we have got some work to do there."
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'Much happier with the car'
Hamilton, who moves to Ferrari at the end of the year, complained on numerous occasions about the characteristics of the previous two cars.
But praising the work put in by Mercedes, he explained: "I'm much happier with the car this year.
"The seat position is finally further rearwards, I've got a better feel for the car approaching the corners.
"But there are other areas that have been improved and it just makes it feel like a race car, for once. The last two cars didn't feel like that.
"It is a really good platform to work on and we have just got to keep our heads down and keep on chasing."
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