Sussex, chasing 316 merely to avoid the follow-on, got off to the worst possible start against an impressive Derbyshire attack when the normally adhesive Ali Orr was out first ball. Playing at a wide delivery he should have left alone, with only two overs to be bowled before lunch, he wafted at it and was caught behind by Brooke Guest.
Captain and star batsman Tom Haines was second out at 36, swinging at a legside delivery from Dustin Melton to give Guest another catch. Danial Ibrahim made just one before he edged the formidable Ben Aitchson to Wayne Madsen at second slip. And Aitchson struck again in his next over when he caught Harrison Ward bang in front of stumps for a duck.
At that stage Sussex were 46 for four and being outplayed by Derbyshire in the battle for the county championship’s wooden spoon. But Brown, watched by his parents and fellow wicketkeeper Oli Carter then put on 142 for the fifth wicket in 40 overs. Carter scored his maiden first-class fifty, though he was out shortly afterwards, caught on the square-leg boundary for 51, and Melton made it two wickets in five balls when he dismissed the wretchedly out of form Delray Rawlins, caught and bowled for a duck off a leading edge.
But Brown, who reached his hundred from 134 balls with 14 fours, went on to reach 150 not out.
Derbyshire had resumed on 371 for five and they lost their sixth wicket to the third ball of the morning. Guest had not added to his 30 runs when he was lbw to the lively Jamie Atkins.
There followed a brisk seventh wicket partnership of 54 between Anuj Dal and Mattie McKiernan, who played a number of handsome strokes before he was caught behind to a delivery from Sean Hunt that surprised him with its bounce.
Ben Aitchison, driving, was caught by Brown at first slip and then Dustin Melton was well taken by Ibrahim at deep backward square-leg. Finally, Edwin Moulton gave Brown his second catch at first slip after it was parried by second slip. Both Atkins and Henry Crocombe finished with four wickets. The Derbyshire total of 465 included 57 extras.