Sussex all-rounder Chris Jordan became the first man to reach 50 Championship wickets for the season on the second day of the Division One game against Derbyshire at Hove.
Jordan reached the landmark when he had Tim Groenewald well caught by Michael Yardy at second slip to give him his third wicket of the day.
Derbyshire, still looking for their first win of the season, were made to battle hard for runs, even though the ball did not swing as generously as it did on the opening day. They were bowled out for 274, conceding a first innings lead of 40 runs.
At stumps Sussex had extended their lead to 51 on 14-1, with opener Chris Nash bowled by Groenewald just before the close.
Derbyshire captain Wayne Madsen was the only specialist batsman to offer strong resistance, batting four minutes short of four hours to compile 97 but there was valuable support lower down the order from 19-year-old Peter Burgoyne, who scored his maiden Championship fifty in only his second match.
Sussex, looking for their fifth win of the season to maintain their challenge for the Championship, took their first wicket of the morning when Jordan had Chesney Hughes caught behind for 16. Three overs later Steve Magoffin had Ben Slater caught behind for 16 and Derbyshire were 40-2.
Luke Wright, operating off a shortened run, put Sussex well on top with two quick wickets. First, he had Shivnarine Chanderpaul brilliantly caught by Jordan, low to his left at first slip, and then dismissed Richard Johnson, who played a weak shot to short cover.
When Jordan had Alex Hughes - making his first-class debut - caught at short leg Derbyshire were in trouble at 103-5.
But Madsen led the recovery, first adding 36 with Tom Poynton and then 78 with Burgoyne, who finished unbeaten on 62 from 105 balls, with eight fours and a six.
Madsen was then seventh out at 217, lbw to Monty Panesar as he played to leg. Groenewald was eighth out to give former Surrey man Jordan (3-73) his landmark and then Matthew Higginbottom, on his Championship debut, was bowled for nine.
Ed Joyce ran out last man Mark Footitt for six but Derbyshire struck a late blow before Luke Wells and nightwatchman Lewis Hatchett saw their side through to stumps.