Nico Rosberg could not believe what he was seeing when he watched back Sebastian Vettel's pole position lap for the Singapore Grand Prix.

Ferrari and Vettel upset the form book in Singapore by taking pole as Mercedes struggled to fifth and sixth. Rosberg felt his lap was a solid attempt but could not believe the extra grip the Ferrari was generating around the 5km circuit.

Asked if he had ever experienced such a drop in performance at one race, Rosberg said: "Not this extreme, because we were so dominant and faster everywhere massively, then to go to the next race, we can't lose 1.4secs on one lap. I just watched Sebastian's on-board - I didn't want to - but I shouted out in the engineering room 'what the hell?!' It seems like he is on a different planet in some corners.

"Everybody is surprised. We don't understand it for now. We tried a lot of things because we understood we had an emergency situation. This morning we tried a lot of things and didn't manage to make progress, we were just lacking grip. If I wasn't looking at the lap times, I would think we would be on pole but then I look at the lap times and I am not on pole."

Rosberg said his main target on Sunday is to close the 53-point gap to Lewis Hamilton.

"The main goal tomorrow is to try and beat Lewis. He is right next to me [on the grid], so the chances are there.

"It is always complicated because we have to score for the team. Of course, Vettel is also a threat to me points-wise because he isn't that far away. We think that it is special here that they are so fast, we still think we will be quick in the races after this. Tomorrow will be a challenge."