Steve Magoffin, bowling from the Kirkstall Lane end, struck Liam Plunkett on the pad, and the England pace bowler scampered through for a leg-bye with partner Tim Bresnan.
Yorkshire’s total thus moved to 250, which gave them a second batting bonus point which, in turn, lifted their season’s tally to 267.
It beat the previous record points haul since the Championship was split into two divisions of 266 by Somerset in 2007, and provided that Surrey do not usurp it by beating Northants at the Oval, which in itself might not be enough, the record will stay with Yorkshire and put a fitting gloss on a champion season.
Rarely has a leg-bye been so warmly applauded as that one moments after start of play, and rarely has a side dominated to the extent that Yorkshire have this summer.
Should they win this game – they go into day three on 55-1 in their second innings, a lead of 58 – they will create a new record, too, for the most wins (11) since the Championship was restructured in 2000.
In the event that Sussex should prevail, it would be Yorkshire’s first Championship defeat at Headingley since Sussex themselves won here in the opening game of 2013.
It is just one of any number of statistics that highlights the strength of the Yorkshire side.
If the day began with the creation of a record, it continued apace with a clatter of wickets.
Two balls after the historic leg-bye, Yorkshire lost three wickets in 10 balls to slip from 250-7 to 251 all-out.
Bresnan edged Magoffin to Chris Jordan at first slip, Jordan then having Jack Brooks taken at second slip by Michael Yardy.
The innings ended when Plunkett lofted Magoffin to mid-on, Magoffin returning his team’s best figures of 4-57.
Just as Magoffin is Sussex’s leading wicket-taker this summer, so Brooks holds that distinction for Yorkshire.
The pace bowler took his 60th Championship wicket of the season when he had Ed Joyce caught behind in the second over.
When Ryan Sidebottom accepted a return chance from Jordan, who perhaps surprisingly opened the batting, Sussex were 3-2 in the fourth over.
It seemed as though a wicket could fall every ball, and it made for compelling entertainment.
Matt Machan produced a flurry of strokes, including two sumptuous off-drives off Brooks, but the bowler had his revenge when he had Machan caught behind with the score on 35.
Yorkshire bagged two more wickets just before lunch, which Sussex took on 79-5, Bresnan having Chris Nash caught behind and Plunkett inducing Luke Wright to edge to first slip. With their position precarious, and perhaps reasoning that attack was the best form of defence against a bowling line-up that would get them out eventually if they simply prodded and poked around, Sussex stepped on it after the break.
Fifty-five runs came from the first 39 balls after lunch before Bresnan got rid of the dangerous Ben Brown, caught hooking at long-leg by Sidebottom.
Brown, who had launched Bresnan’s previous ball for six, made 39 from 29 balls, adding 64 in 51 deliveries with Yardy.
Yardy, making his final first-class appearance, had been applauded on to the field by the Yorkshire team.
The left-hander was twice lucky to get away with Chinese cuts for four off Bresnan, but, for the most part, played well en route to a 56-ball half-century.
Sussex had hit 104 from the first 15 overs after the interval when Yorkshire finally turned the screw, Adil Rashid trapping Ashar Zaidi lbw and Plunkett removing Magoffin caught behind for a golden duck as the visitors slipped to 188-8.
Yardy dragged on to Brooks for 70, made from 81 balls with 13 fours, and Lewis Hatchett was last out for a career-best 25 when he top-edged a sweep off Adam Lyth behind the stumps, Bresnan running back from slip to claim an excellent catch.
Armed with a first-innings lead of three, Yorkshire lost Alex Lees for a golden duck in the second over of their second innings, the opener patting back a return catch to Jordan.
It should have been 7-2, but Gary Ballance – for the second time in the match – edged to the slips and no one got in the way of the ball.
Joyce was at fault in the first innings, and this time Yardy and Joyce left it to each other as the ball flew for four off Magoffin.