Yorkshire 150 and 163 for 5 (Lyth 66, Ballance 36*, Carson 3-35) lead Sussex 221 (Haines 86, Patterson 4-26) by 92 runs
Yorkshire and Sussex were grappling for the ascendancy as their match threatened to dissolve into a three-day dogfight at Hove. Yorkshire's lead was approaching three figures, with the reassuringly solid figure of Gary Ballance booking in for an overnight stay, but Jack Carson, Sussex's 20-year-old offspinner, snapped up three second-innings wickets - including that of England captain Joe Root - to keep tails wagging in the home dressing room.
Yorkshire's fightback began with the ball, Duanne Olivier and Steve Patterson collecting contrasting four-fors as Sussex lost their last seven wicket for 53. Adam Lyth then made his third half-century of the season, to go with two centuries, as Yorkshire overturned a 71-run deficit. But, having carved out a slender advantage through another solid opening stand, a middle-order wobble during the evening session, which included the much-prized wicket of Root, left the game in the balance... and the Ballance.
With Sean Hunt unable to bowl after sustaining a side strain, an even greater weight fell on the shoulders of Ollie Robinson, Sussex's attack leader and a man with the bit between his teeth in pursuit of higher honours. Robinson sent back Lyth during a searching spell but that was his sole success, while George Garton could not find his first-innings spark despite claiming the wicket of Harry Brook.
Garton let slip on the first evening that Robinson had gone into this match declaring his intention of bagging Root twice, as a means of pushing his case to win a Test debut this summer. In the end, he only managed to bowl a total of four balls at the England captain, before Carson had an appeal upheld for caught behind - not that Root appeared to agree with Paul Pollard's decision.
Carson wasn't hanging around, taking off on a dash across the square - "I went for the old Alan Shearer wheel-away, I couldn't really contain my excitement" - and he celebrated each of his wickets with abandon. "Bowling to someone of that calibre, a little bit of nerves can creep in, but the off stump's still the off stump, doesn't matter who it is," he said. "It's just about trying to land it in there as much as I can and let the wicket do the rest."
Born in Northern Ireland but on Sussex's books from the age of 11, Carson has impressed with his flight and control in only his seventh first-class match. Tom Kohler-Cadmore was deceived into walking past one to be stumped and Jonny Tattersall edged to slip late in the day; Carson also saw Lyth dropped at deep square leg off a drag-down. With increasing purchase for spin, his success could point to a pivotal role for Dom Bess in the fourth innings.
For the second day running, it seemed as if Lyth would be the story. At the age of 33, the left-hander may be unlikely to add to his seven Test appearances, but in passing 50 for the fifth time in six innings he continued a fine start to the season. He began this round of the Championship as the competition's leading run-scorer and, although David Bedingham's double-hundred at Chester-le-Street has relegated him to second spot, he was within sight of 500 for the campaign when Robinson speared one into his front pad.
No one has scored 1000 first-class runs before the end of May since Graeme Hick in 1988 - although Nick Compton came close nine years ago, when rain at Worcester delayed him from reaching four figures until June 1. But with five more rounds of the Championship to be played after this one, and runs flowing around the country, there could be several challengers to join a select group, which includes WG Grace, Wally Hammond, Don Bradman and Glenn Turner, as well as Hick.
Although Lyth managed a tally of 108 runs in this match, and Tom Haines held Sussex's first innings together with 86, wickets have fallen in rat-a-tat salvoes throughout, with pace on offer for the seamers and just a smidge of turn.
The day began calmly enough, as Sussex programmed their TomTom to steer them into a first-innings lead. Tom Clark was the more fluent, clipping back-to-back fours off David Willey and swatting away Olivier's short stuff, while Haines set about grinding towards what would have been a third first-class hundred in seven innings. But, having gone past Yorkshire's first-innings 150 three down, the contest suddenly came to life during the second hour.
First Olivier found some inward movement from round the wicket to pluck Clark's off stump though the gate. In the subsequent over, from the Sea End, Bess finally gained reward for his early-season toil as the left-handed Haines was bowled attempting to cut a delivery that drifted in and cramped him for room. It was Bess' first wicket since joining Yorkshire permanently, in his 84th over, and brought a roar of relief - possibly followed by a wince of discomfort, due to a rib problem sustained on the first day.
Bess made light of the issue to send down 25 overs, taking 1 for 55 - modest figures but useful enough in the first innings and indicative of the control he gave Yorkshire as they attempted to parlay a way back into the game. They might have been more impressive still, had Ben Brown, the Sussex captain, not taken him for five fours in 17 balls, including a trio of reverse-biffs to the short boundary.
Olivier picked up his fourth of the innings when Delray Rawlins spooned a drive into the covers, where Root threw himself for a diving catch, but Sussex rallied through Brown, only to then lose their last four wickets for the addition of nine runs. Patterson, the "Beverley Flyer", chugged in from the Cromwell Road End and found a troublesome spot on a length to have Brown lbw and Robinson castled first ball, before coming back after lunch to round up the rest for spick-and-span figures of 4 for 26.

Alan Gardner is a deputy editor at ESPNcricinfo. @alanroderick