Mercedes head of motorsport Toto Wolff has admitted that he is concerned by the pace of Ferrari after Sebastian Vettel won the Malaysian Grand Prix this morning.

The German outpaced the Mercedes pair of Lewis Hamilton and Nico Rosberg as he managed his tyres better in the sweltering conditions at the Sepang International Circuit.

When asked if Ferrari's pace is genuine, Wolff told formula1.com: "Yes, that is worrying. Especially if you have the kind of track temperatures that we had today.

"They have been able to go faster than us over the long runs, so we need to analyse why that was the case. It clearly shows that this year is not going to be an easy one for us - gone are the illusions of a walk in the park."

Wolff added that he did not expect Ferrari to be so strong, after Mercedes dominated at the first race of the season in Australia.

He added: "We definitely did not expect it to happen at that pace. We were pretty dominant in Melbourne. We are always a bit sceptical about our own advantage. That's why we believe that you always have to keep sharp and keep developing in order not to be caught up, and then in two weeks you are actually caught up by a Ferrari.

"We lost the race fair and square. Yes, it was a surprise, but it was also a wake-up call. Which is good."

Hamilton leads the world championship by three points from Vettel, with Rosberg a further seven points behind after two races.