This is a transitional Durham side and their target to avoid the follow-on, 403, looked improbable as they slid to 96 for three in the 36th over.
Sussex broke through in only the third over of the innings when Tom Latham fended a rising ball from Jofra Archer to Harry Finch in the slips. Then, at 43, Cameron Steel cut Danny Briggs to Archer at point for 20. Earlier in the day Steel had been removed from the attack after being no-balled for his second delivery above waist height.
Graham Clark was third out when, attempting to pull, he had his off-stump knocked back by Luke Wells for 27. But then the experienced pair of Smith, 35, who is in his second spell with the club, and Paul Collingwood, 42, pulled the innings round with a stand of 82 in 28 overs.
Collingwood, returning to the side after a calf injury, hit eight fours in his 81-ball 44 and played with confidence against the spin of Briggs and Wells. He appeared a little surprised when he was given out lbw to one from Wells that hit him high on his front pad.
But Smith’s vigil continued and he had batted for four hours for his unbeaten 90 from 216 deliveries, with ten fours. Durham are halfway to ensuring Sussex bat again.
Sussex had resumed on a daunting 439 for five in the morning but Durham were given early encouragement when Chris Rushworth took two wickets with successive deliveries in the third over of the day. First Ben Brown, who had added just two to his overnight 50, skied to the keeper as he attempted to hit the ball over mid-wicket. Then David Wiese was lbw to a pitched-up delivery and Archer was eighth out at 500 when he got a very thick edge to extra-cover for 17.
The bulk of the Sussex batting on the second day was performed by the impressive Michael Burgess. He was 30 not out overnight and as wickets fell at the other end he took the attack to the Durham bowlers. He hit Rushworth for three fours in an over, a lofted drive over extra-cover, a straight drive and a cut. When he reached 91 he became the county’s leading scorer in championship matches this season. But he was caught at backward-point four runs short of his century and without addition Ollie Robinson was bowled by Clarke.