Sebastian Vettel thinks his world championship campaign started to hit the skids in mid September.

Some think the turning point can actually be traced back to his Hockenheim crash in July, or his collision with Lewis Hamilton at Monza.

"It was Singapore for me," the Ferrari driver is quoted by Speed Week.

"From there we did not have the pace to keep up with Mercedes for a couple of races," Vettel explained. "And then there were a few other things that did not help.

"We were unable to score points due to a few mistakes we and I made," he added.

Vettel does admit, however, that crashing out of the lead of his home race at Hockenheim was "the most expensive".

"I've made more mistakes this year even if that was probably the most expensive," he said.

"If you push hard, sometimes you push too hard."

But Vettel says he didn't let that affect him psychologically.

"I do not think about it that often," he said. "It's just part of racing and happens to the others as well.

"That we had problems with our pace and speed in the past few weeks was probably more crucial than that."

Vettel says he will not let the pain of losing the drivers' title affect his motivation to help Ferrari overtake Mercedes in the constructors' battle.

"We're trying to knock Mercedes off the throne, hopefully as a foretaste of next year," he said. "I know I will be able to fight back in a couple of weeks and finish the season as well as possible."