Luis Reece celebrated his county cap with a brilliant career-best 184 to put a large dent in Sussex’s promotion hopes as Derbyshire turned the match at Derby on its head.
Reece had a day to remember as he became only the second Derbyshire player to score 150 and take five wickets in an innings, sharing an opening stand of 274 with skipper Billy Godleman, a county record for any wicket against Sussex.
For the visitors, it was a day to forget as Reece and Godleman tore their bowling apart with Derbyshire closing on 360 for 2 ,267 runs ahead.
That appeared unlikely when 60 from Stiaan Van Zyl and a maiden first-class 50 from George Garton lifted Sussex to 231, a lead of 93, but by stumps, their promotion prospects looked slim.
The batting collapsed before Garton secured what should have been a decent lead only for their bowlers to squander the advantage by losing all discipline between lunch and tea.
Reece and Godleman duly cashed in, leaving Sussex to reflect on a morning of rash shots when clear skies suggested it was a good day for batting.
Although the Derbyshire seamers found some movement, the tone for a chastening day for the visitors was set when Delray Rawlins pulled Reece to mid on.
Ben Brown was caught behind, sparring at the next ball and when Van Zyl was caught on the crease by one that nipped back, it gave Reece five wickets in an innings for the third time this season.
Chris Jordan got an inside edge driving expansively at Fynn Hudson-Prentice and when David Wieise pulled the same bowler to long leg, Susex were only 31 runs ahead.
Garton at least ensured they had something more substantial to bowl at, hitting three sixes off the spinners before his upper-cut to third man gave Dustin Melton his maiden first-class wicket.
The rest of the day turned into a horror show for the Sussex attack which was unrecognisable from the one which had run through Derbyshire the previous day.
A succession of wide, short and overpitched balls were ruthlessly dispatched with 19 from Jordan’s second over the prelude to an afternoon of plunder.
Wieise, who conceded only 18 runs in the first innings, was driven and cut for four consecutive fours by Reece who hit 19 in his second century of the season which came between lunch and tea off only 102 balls.
Reece had faced 189 balls and hit 32 fours and a six when he was run out by a direct hit from cover but the damage he had inflicted on Sussex’s season may be beyond repair.
Sussex head coach Jason Gillespie said: "We've got to dust ourselves off, learn the lessons from today and come in with a good mindset, positive attitude and go out and implement our skills.
"We know we are better than that but we've just had what you could say is a pretty ordinary day, there's no hiding from that, no sugar-coating it. It's been an ordinary day of cricket by us, conversely Derbyshire have had a fantastic day and fair play to them."