Barcelona - Lewis Hamilton shrugged off Ferrari's testing pace on Wednesday while recognising that he and Mercedes faced their toughest challenge yet as they seek to stretch their Formula One domination into a sixth successive season.
Ferrari, overall runner-up last year, led the timesheets for the first two days of testing at Barcelona's Circuit de Catalunya and has also done plenty of laps with its new SF90 car.
Sebastian Vettel, the four times champion who is partnered by young Monegasque Charles Leclerc this year, said on Monday that his Ferrari had been "close to perfection".
Mercedes, winner of both titles for the past five years, has also been pounding out the mileage without setting any eye-catching times.
"They (Ferrari) have been looking great," Hamilton, who will be chasing his sixth title, told reporters. "For us it's been just digging deep, trying to understand the car, Pretty much the same as the beginning of every year.