Sussex 116 for 3 trail Derbyshire 138 (Wiese 4-18)
Reece Topley marked his return to first-class cricket after an absence of more than two years by helping promotion-chasing Sussex bowl Derbyshire out cheaply on the opening day of the match at Derby.
The England seamer, whose career has been blighted by back injuries and was making only his sixth Championship appearance in just over five years, took 2 for 23 as Derbyshire were dismissed for 138.
David Wiese led the Sussex attack with 4 for 18 and only Anuj Dal with 35 gave the home side a semblance of respectability. But Sussex also struggled, losing three cheap wickets, before Stiaan Van Zyl, with an unbeaten 49, and Delray Rawlins carried the visitors to 116 for 3 at the close.
Sussex were initially frustrated by heavy overnight rain, which delayed the start until midday, but their seamers exploited overcast conditions and a grassy pitch to secure maximum bowling points by tea.
Although batting was awkward, there were some indifferent shots as the home side fell away in the afternoon with only five batsmen reaching double figures.
Luis Reece was undone by late movement from Chris Jordan but Billy Godleman aimed a flashing drive that was brilliantly pouched by Phil Salt at second slip to give Topley his first victim in red-ball cricket for 28 months and another smart catch accounted for Wayne Madsen.
Wiese defeated Harvey Hosein's drive before Matt Critchley carved loosely to point and Matt McKiernan lost his off stump to his first ball in first-class cricket.
Topley struck again when Leus du Plooy was caught at second slip after the ball was knocked up by third and after Fynn Hudson-Prentice's miscued pull was well taken by Luke Wells running in from deep square, Rawlins swooped to snare Tony Palladino at backward point.
Dal and championship debutant Dustin Melton held up Sussex for nearly eight overs before Weiss had Dal caught behind but Sussex were soon in trouble as Derbyshire's bowlers also enjoyed the helpful conditions.
Salt got a leading edge to Reece in the fourth over and the allrounder bowled Wells, breaking a bail in the process, before Hudson-Prentice struck with his first ball that came back to trap Will Beer lbw.
At 25 for 3, Sussex were in danger of squandering the advantage their bowlers had secured but van Zyl and Rawlins, through a combination of good shots and good fortune with van Zyl surviving a chance to gully on 41, made sure it was the visitors' day.