Having closed the gap to "zero", Niki Lauda is expecting Ferrari will challenge Mercedes all the way to the final lap of the campaign.
This season has seen a rejuvinated Ferrari team out on track as Sebastian Vettel and Kimi Raikkonen have taken the fight to the Mercedes pairing.
Vettel is the only driver aside from Lewis Hamilton to have won a grand prix while Ferrari is the only team aside from Mercedes to have featured on the podium.
Their improvement, though, has been largely overshadowed by Hamilton's incredible form.
The British racer has claimed three of the opening four race wins and finished second to Vettel to Malaysia, easing him to a healthy 27-point lead in the Drivers' Championship.
Lauda, though, is adamant the battle has only just begun.
"The season is not finished," he told Press Association.
"Ferrari is very strong, there is no question about it, and as a racing team you should never think that nobody can catch you, then you make a big mistake.
"Ferrari has closed the gap from last year to this year to zero.
"I think they increased their engine by about 45 horsepower, so my estimate at the moment is that they have the same engine power as the Mercedes has and now it depends on the car and what the drivers can do – and there will be close racing all the way through the season."
The triple World Champion added: "The best of the rest at the moment is Ferrari, there is no question, and then Williams for me is a little bit disappointing at the moment, but I know that they will bring some upgrades, so then they should be okay."