On the eve of a campaign where Mercedes is expected to make a step forward, Brawn has nothing but praise for his drivers' qualities.
Having seen Rosberg step up his performances alongside Michael Schumacher over the past three seasons, Brawn says more progress from Rosberg gives his outfit the benchmark driver pairing.
"If we are honest, Nico proved himself against Michael," said Brawn during a Mercedes-Benz media event in Melbourne on Thursday.
"I had no question marks about Michael, but I think some people may have done given his retirement and coming back.
"I think Nico is going to have a fresh benchmark in terms of Lewis and I expect them to be very close. I don't expect a big difference between either of them, but that is to be proven.
"It is a big challenge for him to have someone as quick and capable as Lewis in the other car.
"Nico has met some massive challenges - ones that he had with Michael – and I expect him to hold his end up very well.
"I actually think we have got the best driver pairing in F1. They will push each other very hard."
Brawn also feels that Hamilton's arrival at Mercedes over the winter has helped galvanise its efforts.
"Inevitably when someone of the status of Michael leaves the team that is a very big hole to fill," he said. "I think Lewis is filling it perfectly, but in his own style and in his own way.
"I don't want a clone of Michael. I want somebody who does it their own way. He has brought quite a fresh gloss to the team in terms of the way he has approached it, the way he is working with the engineers and I am delighted with the way it has gone so far.
"We have not been in the white heat of battle, and when you go racing you start to learn a lot more about the drivers and the relationship and how it develops.
"That is still to come, but testing has gone as well as I could have expected - not only on the track but in terms of the working relationship that Lewis is building with his team and with his team-mate Nico. That is a vital relationship there.
"I am sure it will have its moment because they are two very competitive drivers. We want them to be competitive but they have to do in a way that is constructive and takes the team forward.
"It is very encouraging so far, and it is really a motivating buzz for the team to be working with Lewis."
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