An unbeaten 75 by the experienced John Morris held up Sussex as Nottinghamshire reached 240-3 in reply to the hosts' impressive 472 at Hove.
Sussex, bidding for a third championship win, were frustrated as Morris batted intelligently to put Notts on course to establish their first target of making 322 to avoid the follow-on.
Sussex were made to work hard for their wickets after James Kirtley struck an early blow by removing Guy Welton for only nine.
Australian Test ace Michael Bevan got through 19 overs of left arm wrist spin, in finishing the day with 1-53, while opening bowler Kirtley also had 1-53 from 17 overs.
Sussex's last four wickets had tumbled for just 17 in seven overs, and Notts began their innings 40 minutes before lunch, with former Surrey opener Darren Bicknell and the uncapped Welton seeking to give their side a sound platform.
But Kirtley broke through in only the sixth over as Welton snicked him low to Tony Cottey at third slip.
Notts lunched on 27-1 and on the resumption Bicknell took nearly an hour to add to his score. He crawled into double figures in 27 overs with a single off Billy Taylor, and the second-wicket pair had added 65 in 30 overs when Jason Gallian fell for 44.
The Notts' skipper was left stranded as Jason Lewry, at mid-off, broke the stumps at the bowler's end as Gallian attempted a needless single off Taylor.
Former Derbyshire and Durham batsman Morris livened up proceedings shortly after tea by straight driving Will House for four before repeating the shot for six next ball.
Morris completed his 50 off 94 balls with five fours and a six, and the third-wicket pair had added 86 in 30 overs when Bevan broke through to remove Bicknell who had occupied the crease for 66 overs.
The opener, attempting to work the ball to leg, got a thick edge as he was beaten off the pitch and Cottey displayed lightning reactions to hold onto the chance at slip.
Morris continued to punish anything loose and hoisted Umer Rashid for six before Usman Afzaal had a let off on nought.
Afzaal lofted a delivery from Bevan to mid off but in a mis-judgement Rashid rushed in too far.
The miss may prove costly and Morris and Afzaal resume today having added 77 useful runs for the fourth wicket.
Sussex earlier seemed poised to push on beyond the 500 mark after resuming on 404-5, but disappointingly lost their last five wickets for only 17 to be bowled out for 472 after 85 minutes.
Australian test pace bowler Paul Rieffel grabbed two of them to finish with 4-85 from 32 overs and Sussex subsided after Notts' skipper Gallian struck the initial blow by removing House for 24.
The former Kent all-rounder, playing in his third championship match of the season, was dismissed in soft fashion as he attempted to pull a long hop and presented an easy catch to Andrew Harris at mid-on.
Rashid followed without addition in the next over from Reiffel, failing to get forward in falling leg before for a duck, and Nick Wilton then became Gallian's second victim for six.
The wicketkeeper called up for his first championship appearance of the season with Andy Patterson and Shaun Humphries having been released, chipped a simple catch to Afzaal at mid on.
Skipper Chris Adams, who had compiled nine boundaries in passing 50 for the fifth time in the championship, had reached 55 when he was sent back by Reiffel.
Gallian swooped to hold a low catch at first slip as Adams pushed forward, and Harris ended the innings by knocking out Lewry's off stump as he shaped to drive.
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