Sebastian Vettel's Malaysian Grand Prix victory was a "wake-up call" for Mercedes, says boss Toto Wolff.
Mercedes dominated the first race of 2015 in Australia after winning 16 of 19 races last year to claim the drivers' and constructors' titles.
However, after Vettel's win for Ferrari, Wolff said: "We didn't expect Ferrari to catch up on the second week.
"So to lose the race fair and square is a surprise and a bit of a wake-up call, which is good for us."
Mercedes were unable to compete with Ferrari in the tropical heat of Sepang because of excessive tyre usage.
"Ferrari deserved to win and from a racing perspective we have to acknowledge they have done great development," Wolff said.
"For F1 it is positive. It is the second race and a second team wins. This is what F1 probably needed."
Mercedes' decisions to make an early stop under the safety car and to race mainly on the 'hard' tyre rather than the faster 'medium' or 'option' were both questioned, but Wolff said they were beaten "fair and square".
"We couldn't match the long-run pace of Ferrari," Wolff said. "It wouldn't be right to say we lost the race rather than they won it.
"If I'm being optimistic I would say Malaysia was difficult for us last year, but then that would be naïve. Ferrari have done well - they have a great car, a great engine, great drivers."
Both Mercedes drivers have said they believe Ferrari could be title contenders this year, but the Italian team say it is too early to judge.
Ferrari technical director James Allison said he did not expect to be able to challenge Mercedes as closely in the next race in China on 12 April.
"I am fairly sure we will have our work cut out in China to do anything like as impressive a job as we have done here," Allison said.