Lewis Hamilton has called on his Mercedes team to up its game, saying he can't create miracles every weekend now that Ferrari has the faster car.

Hamilton still leads the drivers' championship by 17 points thanks to two wins against the odds before F1's summer break. In Germany he took a remarkable win in the wet from the back of the grid after Vettel crashed out of the lead in the rain and in Hungary a wet qualifying session saw him take pole position on a track where Ferrari was clearly faster in the dry. With very few overtaking opportunities at the Hungaroring, Hamilton went on to take his second victory in a row.

In Belgium, Hamilton also took pole position in wet conditions, but was unable to defend against Ferrari's superior engine power and lost the lead to Vettel on the opening lap. Hamilton said he is used to being the underdog and creating chances, but warned he would not be able to hold off the threat from Ferrari if things continue in the same vein.

"That's how my life's always been -- I started with a really old go-kart and I used to beat people with much better equipment," he said. "My dad used to call it a four-poster bed, he said I could drive anything. So naturally I feel I can eke a bit more out of it, and I have been in recent races, and beat a faster car.

"But there is only a certain amount I can do -- I can't always create miracles. There are going to be times like today where it doesn't work. But there are still eight races to go and a lot of positives to take into those races, we have just got to keep working on the car and the tyres and optimise that. We can still beat them at races, I just don't know which ones it is going to be."

Lewis Hamilton holds a 17 point lead over Sebastian Vettel in the championship. Mark Thompson/Getty Images

With the next two races coming at the high-speed Monza and Mercedes' bogey track Singapore, Hamilton said the title battle is only going to become more difficult as the season progresses.

"If it hadn't rained in Hockenheim we wouldn't have won. If it hadn't rained in Hungary we wouldn't have won. And obviously he won today but if it hadn't rained yesterday we probably wouldn't have started first and I don't know if we would have been able to tow him down that back straight. It might have been similar to last year but just in reverse. So the rain creates opportunity, but we can't just rely on that.

"We have to improve our performance so we can maximise on days like today in the dry conditions. These races coming up, I imagine it is going to be hot next week, hot in Singapore -- the rain there is always welcome -- and then I don't know where we have got after that. This is definitely the hardest season and it will continue to get harder and harder throughout."