Sussex 66 for 3 trail Middlesex 269 (Robinson 4-46, Magoffin 3-61) by 203 runs
An injury to Ajmal Shahzad put a dampener on Sussex's opening day against Middlesex after they dismissed the LV= County Championship leaders relatively cheaply at Hove.
Sussex, who came into the match just three points behind their rivals, won the toss and had Middlesex at 121 for 5 with Shahzad having taken 2 for 28.
But the former Yorkshire bowler left the field with a pectoral injury and the visitors recovered somewhat to post 269 with Ollie Robinson taking 4 for 46 and Steve Magoffin adding 3 for 61.
There were also a startling 62 extras in the Middlesex total - by far the highest contributor.
Sussex then lost Chris Nash, Matt Machan and Michael Yardy in struggling to 66 for 3 in reply in 16 overs batting in the evening sunshine.
An overcast, hazy morning prompted Sussex's decision to bowl first and Shahzad helped Magoffin to set the early tone by reducing Middlesex to 10 for 2 against the new ball.
He then returned before the lunch interval to have James Franklin taken at second slip for a duck soon after Robinson had cut short an aggressive, counter-attacking 38 from Adam Voges, who hit seven fours.
Nick Compton battled hard to get Middlesex through to lunch on 87 for 4, despite being beaten on several occasions outside off stump.
Sussex were handicapped when Shahzad left the field early in the afternoon session after bowling two balls of his 10th over but Robinson and Magoffin both bowled well to keep Middlesex under the cosh.
Compton had only converted his lunchtime 22 not out into a dogged 30 before he edged Robinson to Yardy at second slip and then Magoffin finally got proper reward for his perseverance and skill by dismissing John Simpson and Neil Dexter in successive overs.
James Harris was then undone by a ball from Robinson that leapt alarmingly at his throat and which he gloved through to wicketkeeper Ben Brown.
Matt Hobden got Ollie Rayner leg-before for 17 but Toby Roland-Jones and Steven Finn added an invaluable 38 in seven overs for the last wicket until the hard-hitting Roland-Jones holed out to deep mid-wicket off Robinson for a 30-ball 34.
In reply, Nash went for 23 as he inside-edged Harris onto his stumps in the fifth over while Machan edged Finn to second slip on 13 and Roland-Jones pinned Yardy leg-before for nine.
Middlesex managing director of cricket Angus Fraser, said: ``It's difficult to decide where this match is at the moment. We scored 269 but had a top score of only 38 and benefited from those 60 extras.
``The pitch is hard but cracked in places so the odd ball will do something and it might do more as the game goes on. Has it been good bowling or poor batting so far? It's been a strange sort of day.''
Sussex head coach Mark Robinson added: ``Ajmal Shahzad's injury hampered us a lot today. He has strained a pectoral muscle just below his left shoulder, and we need to see how it is in the morning before we can assess how bad the injury is. But he came off because he couldn't bowl with it, not as a precaution."