Yorkshire's hopes of closing the gap on leaders Durham at the top of LV= County Championship Division One were kept in check after a flurry of late wickets by Sussex.
Seamer James Anyon struck twice and there was a maiden first-class wicket for left-arm spinner Ashar Zaidi as second-placed Yorkshire ended the second day on 246-4, still trailing Sussex's first-innings total of 292 by 46.
They looked to be on their way to building a substantial lead when Adam Lyth and Kane Williamson were adding 164 for the second wicket after the early loss of Phil Jaques as Yorkshire replied to Sussex's 292.
However, opener Lyth was out in the 90s for the ninth time in his career while Andrew Gale and Jonny Bairstow fell to Anyon as Sussex finally got some reward for their perseverance on a docile pitch offering little pace or sideways movement once the new ball had lost its hardness.
Their best bowler was once again the country's leading wicket-taker Steve Magoffin, who snared fellow Australian Jaques during an excellent new-ball spell of 1-16 from eight overs. The dependable Magoffin bowled 15 maidens in his 25 overs in four spells at a cost of just 29 runs.
Jaques had passed 15,000 career runs on his way to 21 when Magoffin, having bowled a succession of out-swingers, brought one back in to trap him in front of middle stump.
That was to be Sussex's last success for nearly three hours as Lyth and Williamson built a solid platform during the afternoon session.
Neither offered a chance but they were never able to score at more than three runs an over on a slow pitch that made timing strokes difficult.
Nonetheless Lyth looked on course for his second Championship hundred of the season when he tried to run a ball through the off side but gave a simple catch to Matt Prior at slip, having faced 205 balls and hit 14 fours.
Zaidi's exuberant celebrations were understandable. It was his first first-class wicket for four years since he played for Islamabad in Pakistan's domestic competition, before coming to England to play club cricket for Accrington.
Anyon took his first wicket when skipper Andrew Gale was drawn into playing at an outswinger and Ben Brown dived in front of slip to take a good catch. Anyon then ripped out Bairstow's middle stump as the England man drove loosely, having struck two boundaries earlier in the over.
Williamson was 80 not out at stumps and nightwatchman Steve Patterson successfully negotiated five overs before bad light forced the players off with two overs unbowled.
Earlier, Sussex's last-wicket pair Ben Brown and Lewis Hatchett had added 28 before Hatchett was taken by Lyth at second slip to give Ryan Sidebottom his fourth wicket. Brown, having been dropped on 14 and 74, finished unbeaten on 84.