Valtteri Bottas has discovered the secret of beating Lewis Hamilton.

That is the belief of Nico Rosberg, who finally beat Hamilton to the world title in 2016 and then promptly quit Mercedes and the sport.

His successor was Bottas, who struggled alongside Hamilton in 2017 and 2018 but this year is already a point ahead of his teammate at the top of the championship after four races.

Rosberg, who senses an "interesting dynamic" between the Mercedes drivers this year, said the key to beating Hamilton is to not provoke him.

"You should never annoy Lewis," he told SID news agency. "If he gets angry, then he gets more motivated and concentrated and bites like a terrier.

"Valtteri has got the hang of something that I only found in my last season," Rosberg added.

Rosberg said Hamilton's attempt to win the wheel-to-wheel battle with Bottas at the first corner in Baku was "tame".

Even Hamilton admits he was too "friendly". "I basically gave it to him," said the Briton.

That could now change in Barcelona, with F1 legend Gerhard Berger saying Hamilton is on a level "similar to that of Ayrton Senna".

But Berger also told Speed Week: "I have to say that I am deeply impressed with Valtteri Bottas.

"He's a cool, very nice guy. Calm, but very fast," he said.

"Hamilton's advantage is his patience. He does not want to win in the first corner. He can wait -- and then win."