Mercedes expect Ferrari to bounce back at this weekend's Bahrain Grand Prix after the champions dominated the opening race of the season.
The Ferraris were fourth and fifth in Melbourne on 17 March, a minute behind Mercedes' winner Valtteri Bottas.
Mercedes boss Toto Wolff said Ferrari showed in pre-season testing they were stronger than they looked in Australia.
"We've seen the potential of Ferrari's package in Barcelona; we expect them to come back strong in Bahrain," he said.
Wolff added that he expected Red Bull, who finished third with Max Verstappen at Albert Park, to be "in the mix as well".
"Claiming the maximum 44 points race from the first race was a fantastic result," Wolff said.
"But the fight has only just begun: Ferrari will try everything they can to hit back and Melbourne showed that Red Bull will have something to say in the fight, too.
"After the Barcelona test, we felt that we were the challengers (to Ferrari). Whatever the Melbourne result says, our mindset hasn't changed since then.
"One race doesn't determine the pecking order for the rest of the season. We need to extract every bit of performance from our package and keep on working hard to improve the car over the weekend to be competitive."
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Hamilton, who took pole in Australia but was beaten off the line by Bottas and then fell back following an early pit stop and some light damage to his car, said he had been surprised by Mercedes' dominance over Ferrari in Australia.
"I think everyone is," he said after the race in Melbourne. "No-one was expecting to have a gap like that. What was shown was that they were ahead and it wasn't the case for this weekend.
"We did our normal job. I'm sure they will come back strong so we have to stay on our toes."
Ferrari team principal Mattia Binotto said: "In Bahrain, as a team, we will have to ensure that we have understood and rectified the areas where we were weak in Australia, which therefore meant we were unable to fully exploit our car's potential.
"In Bahrain, we expect to see the effect of the corrections we have made, although we are well aware that our competitors will once again be very strong. With that in mind, we are keen to get back on track and face up to them."
The concern will be if Ferrari fail to post an improved showing in Bahrain, which is a very different type of track from Albert Park, requiring different qualities from a car.
If Ferrari cannot be competitive at the Sakhir track, fears will grow that Mercedes could dominate the season.