Red Bull team principal Christian Horner described the Mercedes W10 as appearing "stiff and difficult to drive", despite Lewis Hamilton and Valtteri Bottas ending eight tenths of a second clear of the field in Friday practice for the Australian Grand Prix.
Hamilton topped both the FP1 and FP2 timesheets on Friday, pouring doubt on the Silver Arrows' own predictions of the F1 pecking order in 2019.
Ferrari certainly did not appear to run to their full potential, Sebastian Vettel and Charles Leclerc going fifth and ninth-fastest respectively.
???? “I really have a positive buzz from driving the car today. Driving around here, it’s such a great track and with these new cars, the flow is just… it’s beautiful.”@LewisHamilton on Friday’s running at the #AusGP ????pic.twitter.com/Q4lZ2wYmng— Mercedes-AMG F1 (@MercedesAMGF1) March 15, 2019
Bottas suffered a number of moments, but ended the day within four hundredths of a second of Hamilton.
And Horner believes the advantage on the timesheets will not be repeated when qualifying ends on Saturday.
"Long runs we look pretty sensible," Horner told Sky Sports.
"I think the one-lap pace of the Mercedes in [FP2] looked pretty impressive, but the car looks stiff and difficult to drive, so whether that's sustainable for a Grand Prix, I don't know.
"Ferrari looked like they under-delivered to what we thought they had in testing, and our guys both had pretty decent runs.