Somerset collapsed to 244 all out after opting to bat first on day one against Sussex, who closed on 174-2 in reply with Michael Yardy on 94 not out.
Marcus Trescothick and Nick Compton both went without scoring in the first two overs after Somerset chose to bat on a quick, green pitch at Taunton.
Skipper Trescothick edged behind off James Anyon to register his third straight duck, having failed to register a run during T20 victories over Gloucestershire and Northamptonshire.
Australian seamer Steve Magoffin added his second wicket, that of Alviro Petersen caught by wicketkeeper Ben Brown, to leave the home side on 33-3.
James Hildreth hit 11 fours in his 66, the top score of the innings, before Hildreth and Jos Buttler (11) departed prior to lunch and the wickets kept tumbling in the afternoon.
From 152-7, Craig Kieswetter (55) and Alfonso Thomas (33) put on 52 for the eighth wicket to take Somerset past 200 and a bonus point but Kieswetter then ran himself out, beaten by James Anyon's throw from mid-on.
Magoffin finished with 4-65 to take his tally to 41 in Division One this season, while his fellow seamers Anyon (3-61) and Jordan (2-82) offered valuable support.
Sussex were reduced to 8-2 in reply with Jamie Overton (1-30) removing Luke Wells (4) and Steve Kirby (1-22) accounting for Chris Nash (4) during their respective opening spells.
But Yardy and Matt Machan (58no) batted throughout the remainder of the day to leave Sussex only 70 runs adrift at the close.
Yardy has already hit 17 fours in a 79-ball counter-attack and will resume on day two needing another six runs to complete his 20th first-class hundred.
Sussex are unbeaten in the County Championship this season and came into the match five points behind Division One leaders Yorkshire, while Somerset earned their first win last time out against Derbyshire and sit in sixth place.