BARCELONA • While critics point to Mercedes' five-year dominance of Formula One as the reason why they remain favourites to retain their drivers' and constructors' championship titles, Ferrari's form in pre-season testing has given Lewis Hamilton cause for concern.
The five-time world champion told BBC Sport yesterday that "it appears it's going to be even more of a challenge for us this year".
He added: "Ferrari are very, very strong right now, as you've seen."
His optimism has been kept in check by Ferrari's new recruit Charles Leclerc, who kept the Scuderia on top of the timesheets, and did more laps than any other driver on the second day of F1's pre-season testing in Spain on Tuesday.
After teammate Sebastian Vettel led the way on Monday with the fastest time (1min 18.161sec) and most laps (169), Leclerc slotted in seamlessly with a time not far off.
He produced a best time of 1:18.247 and did 157 laps at the Circuit de Catalunya in Barcelona.
"I quickly felt comfortable with the SF90 and I have to say I really enjoyed myself," said the 21-year-old. "Let's hope we keep going like this over the next few days."
Hamilton, working through the Mercedes testing programme, did one more lap than Leclerc in the morning stint before handing over to teammate Valtteri Bottas.
Between them, the Mercedes drivers covered 163 laps - the most by any team on Tuesday - without their times standing out from the crowd as the champions focused on set-up and long-run reliability.
"We were focusing on working through our run plan and we got through everything we wanted," said Hamilton, who ended up 10th-fastest with a time of 1:19.928.
"It's good that we're getting in a lot of mileage and we will try to increase that over the next days as we continue to discover the characteristics of this car."