Warwickshire's bright start to the season continued at Chester-le-Street, where winter recruit William Porterfield punished Durham wicketkeeper Michael Richardson for an early missed chance as the visiting team reached 345 for 7.
Two quick wickets had turned 71 without loss into 73 for 2 as Durham made a double breakthrough after 75 minutes and it should have been 77 for 3 but Richardson, standing in again for the injured Phil Mustard, spilled a catch off Callum Thorp's bowling.
Although Richardson combined with Graham Onions to remove the threat of Mohammad Yousuf when the former Pakistan Test player had made 25, Porterfield made the most of his luck, reaching 87 before he was leg before to spinner Scott Borthwick.
Thorp had made the first breakthrough when Ian Westwood was caught behind for 46. Varun Chopra, with two double hundreds already this season, then fell for 23 when he chipped Ruel Brathwaite to Ben Stokes.
Stokes, whose bowling has been restricted by an ankle problem since he took 6 for 68 against Hampshire two weeks ago, was pressed into service as fourth seamer with Mitch Claydon left out but conceded 50 runs in five wicketless overs.
Lancashire, joint leaders with Warwickshire after both won their opening two matches, likewise maintained their form on the first day against Sussex at Hove, where Paul Horton and Stephen Moore combined in the county's biggest first-wicket stand since September 2008, putting on 129 in 36 overs before Moore, one run shy of a half-century, was leg before to Luke Wright, making his first appearance since suffering a knee injury with England in the World Cup.
Horton hit 13 boundaries and looked in exceptional form but was on 78 when he top-edged a pull against Rana Naved-ul-Hasan, first slip Ed Joyce getting under the catch. Mark Chilton was run out after putting on 82 with Karl Brown for the third wicket and Monty Panesar was rewarded for his perseverance when Steven Croft paddled a catch to short leg but Sussex did themselves no favours by donating 36 free runs from no-balls.
James Harris, feted as one of the next generation of England fast bowlers, demonstrated his prowess with the bat at Chelmsford, scoring his fifth first-class fifty. He finished his day by dismissing Alastair Cook for five as Essex closed on 13 for 1 in reply to 282.