Lewis Hamilton fears that, despite steering his Mercedes to victory in Sunday's Belgian Grand Prix, Ferrari have a faster car and he faces an uphill struggle to catch title leader Sebastian Vettel.
The 32-year-old Briton, who reeled off his fifth win of the year to reduce Vettel's lead to seven points with eight races remaining, said he jad found it difficult to resist the German's attacks.
"I think Ferrari were ultimately quicker. I was just able to keep them at bay," said Hamilton. "But if our cars were reversed, I don't think I would have been able to hold as close as he did.
"If anyone's out there thinking we have the best car this year then they need to think again because it's not the case... We might have the upper hand in power, but that's not enough - we have to keep improving."
Heading into Ferrari's home race at the Italian Grand Prix, Hamilton knows he needs to make the most of Mercedes marginal power advantage in his bid to take the championship lead for the first time this year.
Mercedes introduced an upgraded engine at Spa-Francorchamps and their speed in straight lines on the long straights was critical to the result of qualifying and the race.
"I think we have the upper hand power-wise, but we've got to keep improving," added Hamilton.
"The pressure is on. The next race, package-wise, should be similar to this weekend, but when we get to Singapore that's really where the test is going to be - and where Ferrari should be really fast, as they were in Hungary..."
Hamilton added: "Ferrari have had the most consistent season and, while we've had a solid and well put together weekend, it was only just enough to stay ahead.
"I hope we have more to come and we need more to come in order to win this thing for sure. It's going to take everything from every single one of us to finish these next eight races and come out on top.
"That's how a championship should be so I'm really looking forward to that challenge. It's going to go right down to the wire."
Mercedes boss Toto Wolff admitted his team were "surprised" by Ferrari's speed and challenge.
"They have done a good job in bringing an upgrade package that works - this is a track that shouldn't suit them, like Silverstone, but they were much closer than expected.
"We just have to keep our development scope steep and continue to bring bits on the car and deliver faultlessly."