Essex lost their first wicket in the third over when Varun Chopra edged a Matthew Nicholson out-swinger but Pettini and the in-form Bopara took advantage of some wayward bowling to seize control.
Bresnan is more of a traditional swinger than Yorkshire team-mate Ajmal Shahzad or Chris Tremlett, which works in his favour, although the Waca is traditionally the fastest and bounciest pitch in Australia, which will suit the bowling styles of the other two seamers.