Graham Onions carried on from his form yesterday and first dismissed Wells for 17 with Mustard taking the catch behind the stumps and then in his next over claimed the wicket of Hamilton Brown for 4 with Mustard again taking the catch, this time in more spectacular fashion with a dive to his right to leave the visitors five wickets down.
Mitch Claydon then took the 6th wicket when Anyon hit one back to the paceman to depart after making 19.
Usman Arshad then came into the attack and got a roll on, showing his potential taking the next three wickets, firstly trapping debutant Finch, then dismissing Beer and Magoffin who both edged behind to Mustard and Sussex were suddenly 111-9.
Mitch Claydon then wrapped things up when he took the final Sussex wicket, clean bowling Hatchett in the 45th over to have Sussex all out for 112.
Durham, holding a lead of 133, again started shakily with Keaton Jennings the first to find his way back to the pavilion, contributing 10 before he was caught by Nash off Magoffin.
Durham’s highest run scorer from their first innings looked good early until he became the second wicket to fall, trapped lbw by Anyon to have Durham 31-2.
Smith and Borthwick then looked to build on the Durham lead but Borthwick’s innings ended early when he edged Anyon to Brown on 10.
Smith then combined with Richardson and the pair got the Durham lead past 200 to 217 before Smith became the next batsmen to edge behind with the number four giving Hatchett his first wicket to depart for 22.
Richardson then became the third Durham batsmen in a row to knick to the keeper with a faint edge off Magoffin leaving Durham 90-5 with a lead of 223.
The experienced duo of Collingwood and Mustard were then at the crease and held their composure during a tricky period for Durham and the pair steadied the ship to see Durham through to tea at 116-5 with a lead of 249.
They carried on in the afternoon session and put together a superb 93 run stand, taking the lead past 300 before Collingwood was trapped lbw for 45 by Nash with just 10 overs to play in the day.
Mustard continued at the crease, passsing 50 (of 119 balls and 8 fours) and saw the day out to finish on 57no with Usman Arshad 16no and Durham 212-6 with a lead of 345.