Mercedes and McLaren have bounced back from a difficult morning in the second F1 practice session of the season in Bahrain.
Nico Rosberg proved that he is unlikely to be awestruck by Michael Schumacher's arrival at the Mercedes team (ex-Brawn) by posting the fastest time, while Lewis Hamilton reversed the McLaren team standings from the first session by claiming second.
Schumacher ended the session in third spot, 0.5sec behind Rosberg, while Button was fourth.
It was a better session for Red Bull and Williams - Sebastian Vettel and Nico Hulkenberg were fifth and sixth respectively - but the Ferraris were working on heavy-fuel runs. Felipe Massa was seventh, two places clear of team-mate Fernando Alonso.
The new teams continued to struggle. Timo Glock's Virgin was the fastest newcomer 5.4sec off the fastest time, and HRT faced problems with its untested machine; parts could be seen flying off the right-rear of Bruno Senna's car at the end of the main straight, while his team-mate Karun Chandhok has failed to get in a lap all day.