Button wary of Mercedes threat
Jenson Button believes Nico Rosberg's win in China on Sunday has paved the way for Mercedes to become championship contenders this season.
After collecting just one point from the opening two races, the Brackley-based marque where Button spent seven seasons - six as Honda and one in winning the title with Brawn in 2009 - finally proved their potential in Shanghai.
In his 111th race, Rosberg followed up on his maiden pole with a debut victory, finishing a comfortable 20 seconds ahead of Button in his McLaren.
Mercedes took advantage of the cooler climate in China as their tyres found the perfect operating window, so it remains to be seen in the heat of Bahrain this weekend whether Rosberg and team-mate Michael Schumacher can again dial in their cars.
Whatever unfolds, Button feels with the team's resources and the technical staff behind the scenes, they are in the hunt for the bigger prizes.
"They'll be quick," said Button.
"In qualifying pace they are phenomenal, and they have been all year.
"The first time Nico got it together in qualifying was in China, so they are going to definitely be competitive, and it's great to see that they are.
"I spent a lot of years with that team - most of my career was with that team - so I am very happy for them they've achieved a grand prix victory this year.
"There's a great bunch of people there, and people that went back to the team as well that I used to work with, like Geoff Willis, so that does obviously pose a threat to us in the championship.
"As I say, I'm happy for them, but that's done now and we're fighting."
Button is refusing to write off Red Bull either, even though they have looked far from reigning champions in the three races so far, certainly in qualifying.
Neither Sebastian Vettel nor Mark Webber have come close to the front row, with team boss Christian Horner insisting qualifying is the one area they have to crack.
In the race, however, Red Bull have been strong, with Button fully expecting them to eventually come good.
"Mercedes will be tough competitors, but they won't be the only ones," added Button, currently two points behind team-mate Lewis Hamilton in the championship standings.
"They have shown their pace in quali, also in the race and the strength of their team.
"They didn't really do much in qualifying in China, and probably they didn't have their best day in the race.
"But they still finished fourth and fifth, so are picking up big points when their car isn't as competitive as they would like.
"So I would say those two teams at the moment are the biggest threat because they consistently show their pace.
"Whether they get the result or not is a different story."