Durham 103 (Robinson 5-29) and 220 for 4 (Steel 104*) lead Sussex 122 (Rushworth 8-51) by 201 runs

Sussex ran aground against the unwavering qualities of Chris Rushworth at Chester-le-Street as a day that should have confirmed them as serious promotion challengers instead threatened to undermine their challenge at a critical time.

Having dismissed Durham for 103, Sussex should have observed a day of blue skies and imagined that the match might be in their grasp by nightfall, only for Rushworth, with subtle variations in nibbling but far from impossible conditions, to begin an extraordinary turnaround.

As rugged as the Durham Heritage Coast, he turned in a redoubtable shift of eight for 51 against somewhat fatalistic batting, the second best figures of his career. What should have been a potentially matchwinning lead instead amounted to a paltry 19 runs.

Cameron Steel's composed, unbeaten century - only Durham's fifth of a difficult batting summer (they are hardly alone in that) - then impressed upon Sussex what might have as Durham built a lead of 201 with six wickets remaining. It is a definite, if by no means impregnable, advantage.

This was a naïve batting display by Sussex who hit out against Rushworth's persistent probing as if fearing a ghost in a fog. Their promotion tilt has gathered pace despite a top six hardly replete with pedigree and this was a day when more nous would have served them well. As one of only three frontline seamers, Rushworth bore a heavy burden. "He keeps coming," said Sussex's Ollie Robinson afterwards. And no wonder.

Rushworth is not just a county cricketer; he is a heritage cricketer, a player who with every insistent delivery represents the traditions and the culture of the region that he represents. Such qualities have been indispensable during Durham's recent travails and when his benefit season was announced at close of play it did not seem, as so often, an anachronism, but a richly deserved recognition to a loyal servant who given good fortune can bundle in for a good few years yet.

This Chester-le-Street pitch has been known to flatten out in the third and fourth innings this season (a timing that is expressed in these parts as: "When we can't get any batting bonus points" - they have two). Durham have overcome Derbyshire and Leicestershire from unpromising positions so they will be aware that Sussex could do the same.

Durham, seven down overnight, had been duly rounded up for 103, but the first day, according to the locals, had been a foul, malevolent day with the biggest black cloud seen over the ground since the ECB relegated them for financial difficulties. Sussex, by comparison, batted in conditions where, as AE Housman had it, "Up from the eastern sea / Soars the delightful day." Just an hour's defiance against the new ball could have made all the difference.

Remorse, though, took hold instead as Rushworth set to work. Tom Haines fell for nought, fifth ball, an ugly poke to third slip; his fellow opener, Phil Salt, attempting to dominate from the outset, came a stride down to clip in front of square and fell to an excellent catch by Graham Clark.

Luke Wells was bowled through the gate by Matt Salisbury next ball, which did'nt just continue a lean season but was the moment that for much of the innings seemed designed to deny the persistent Rushworth all ten until David Wiese, the last wicket to fall, was lbw to give Salisbury a second wicket.

Most of Rushworth's wickets came to deliveries cutting back, such as the one that struck Harry Finch's off stump as he offered no stroke, the bowler's 400th first-class wicket for Durham. Ben Brown was lbw to one that might have been a tad igh. But tere were giveaways, too, such as Michael Burgess' pull to a fielder in the deep. For once, there was no Sussex late-order recovery, Will Smith expertly snaffling a second catch at point to dismiss Chris Jordan, Jofra Archer outdone first ball by one that left him and Ollie Robinson's glide knocked on by the wicketkeeper to first slip where Paul Collingwood proved that your reflexes don't go as quickly as some people think.

In response, Steel and Alex Lees put on 72 for the first wicket before Lees was clearly aggrieved to be given out caught behind on 43 off the bowling of Robinson. He left with half-a-dozen glares back at the umpire; "never look back" is a decent life motto, especially if you are a county batsman wanting to avoid a fine. Archer, who bowled impatiently, then accounted for Smith and Clark, but Sussex's frustration returned when Steel was given a life on 95 when he top edged a delivery from Jordan, but Salt, running backwards from slip, slipped as he misjudged the catch.

For all Steel's contribution, the day belonged to Rushworth. "It has been a good day: personal milestones, good news and putting us in a winning position," he said. "If you looked at the state of the game this morning and you told someone what was going to happen they wouldn't believe you. It has been an incredible day of cricket."