Middlesex 138 and 61 for 4 (Robinson 4-23) trail Sussex 481 for 9 dec (Van Zyl 173, Brown 107, Salt 50, Beer 50) by 282 runs
Sussex pace bowler Ollie Robinson left Middlesex facing the prospect of their heaviest County Championship defeat of the modern era after a rain-affected third day at Lord's
The right-arm seamer tore out the heart out of the home side's top order with figures of 4 for 23, which included a burst of 3 for 8 in 14 balls.
When the weather closed in to provide temporary respite for the beleaguered Seaxes they were 61 for 4 still needing 282 to make Sussex bat again.
Perhaps more pertinently, Stuart Law's side require a further 51 to better their loss by an innings and 232 runs to Sussex at Lord's in 2005 - their worst defeat against a county side since before the outbreak of World War II.
Robinson, in his first match since injuring his shoulder against Durham in April, had taken three wickets on the first day as the Lord's tenants were hustled out for 138. In more seamer friendly conditions he was close to unplayable second time around.
The 25-year-old and his new-ball partner Mir Hamza set Middlesex openers Max Holden and Sam Robson a searching examination in the morning gloom.
Both bowlers beat the bat a number of times and it was no surprise when Holden edged a ball leaving him a touch on the off-stump line to Luke Wells at fourth slip.
Holden will have been left doubly frustrated by the fact just four balls later, rain and bad light intervened for the first time, driving the players off for an early lunch.
The shortened first session meant Robinson had plenty of energy in reserve to take up where he left off upon the resumption and he did so to devastating effect.
Moving the ball both ways off the seam, he castled Robson with one which trapped the batsman on the crease and bowled him through the gate.
Home skipper Dawid Malan was then undone by one which went the other way, feathering the thinnest of edges to Chris Jordan at first slip.
Worse was to come for Middlesex when Stevie Eskinazi poked tentatively at another ball on a nagging off-stump line to give Wells his second catch of the day.
Nick Gubbins and James Harris staved off any further drama before the rain came again to prevent any further play.