The German, who has scored a maximum 50 points after winning in Australia and Bahrain, told reporters he had no illusions about the challenge ahead.
"We know Ferrari are super close, we saw it in qualifying and we need to keep pushing," said Mercedes driver Rosberg. "They haven't shown what they are able to do yet in these first two races.
"They've had so many mishaps that have cost them dearly so we haven't seen the real Ferrari yet. We need to be careful, they are coming at us strong."
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While Mercedes have won the last eight races, and Rosberg five in a row, there was evidence to suggest Ferrari have closed the gap and could have won in Australia and Bahrain.
In Melbourne, Sebastian Vettel and Kimi Raikkonen jumped Rosberg and triple champion team mate Lewis Hamilton at the start and potentially had a winning strategy until the race was stopped and re-started after Fernando Alonso's big crash.
Vettel finished third after a wrong tyre strategy call while Raikkonen retired with flames flickering from the airbox of his car in what looked like a turbo failure.
In Bahrain, four-times world champion Vettel qualified in third place but retired before the start with a power unit failure.
Raikkonen then made a poor start from fourth but still fought back to finish second, using exactly the same tyre strategy as Rosberg, just 10 seconds behind.
"It's clear we would have seen a different race if Sebastian had not been forced to retire before the start," commented Mercedes motorsport director Toto Wolff.
Ferrari principal Maurizio Arrivabene felt Raikkonen could have won with a better start even though Rosberg, now 17 points clear of Hamilton and 32 ahead of Raikkonen, controlled the pace from the front all evening.
"Kimi had a bit of a problem at the start and I think that penalised him quite a lot...maybe he compromised the victory of the race," said the Italian.
"The way that Kimi drove during the race was spectacular, absolutely spectacular."
(Editing by Tony Jimenez)
