Northamptonshire 273 and 212 for 4 (Vasconcelos 88, Newton 54) lead Sussex 106 (Sanderson 6 for 37) by 379 runs
Northamptonshire are on course to claim their first County Championship win of the season after bowling out Sussex for their lowest total for 12 years.
Bottom of the second division going into the fixture, Northamptonshire ended day two at Hove with an overall lead of 379 on 212 for 4 in their second innings after Sussex had earlier been dismissed for 106, their lowest score since May 2007 when they made 102 against Kent at Canterbury - a season when they went on to become county champions.
They had no answer to the unrelenting accuracy of Northamptonshire's four seamers led by Ben Sanderson who finished with 6 for 37, his best figures of the season. They found the right length throughout and a pitch offering some seam movement and swing.
Northants did not enforce the follow-on and when they batted again Ricardo Vasconcelos, who scored 88, and Rob Newton, who reached 54, added 108 for the first wicket. Abi Sakande picked up two wickets but Sussex had long since been consigned to damage limitation. Their only hope now is to at least show a bit more resolve when they bat again.
Sussex had resumed on 7 for 2 and they soon lost overnight batsmen Luke Wells and Aaron Thomason in successive overs. Brett Hutton picked up Wells and Sanderson claimed his first wicket of the day when Thomason edged an away-swinger to third slip, just as Wells had done.
It set the tone for a dispiriting morning for Sussex who were 26 for 5 as Sanderson struck again to remove Laurie Evans. Evans was also beaten by late movement and edged to first slip. Ben Brown and Delray Rawlins staged a mini recovery to take the score to 49 before Luke Procter straightened one nicely and Brown 10 edged behind.
Rawlins rode his luck at times but briefly broke the shackles to take successive boundaries off Hutton before Sanderson returned to have him taken a second slip for 31. While Sanderson, Hutton and Procter shared the spoils they were backed up by Nathan Buck, whose six overs contained four maidens.
After lunch, Will Beer - batting at No.9 having opened in his last three games - was lbw to Hutton for one before Sanderson finished things off. David Wiese, who helped Rawlins add 34 for the seventh wicket, was caught behind and Sakande edged to third slip in the next over.
Northants batted again with a lead of 163 and by tea had extended that to 275. Vasconcelos and Newton reached half-centuries off successive balls with Newton hitting Beer for six to get there.
Sussex made a breakthrough with the first ball after the resumption when Newton edged to slip to give Ollie Robinson his seventh wicket of the match and there was double success for Sakande who had Alex Wakely caught behind off an inside edge before pinning Vasconcelos for 88 after the South African had struck 13 fours.
Temba Bavuma smashed a waist-high full toss from Rawlins to deep mid-wicket just before the close but it was a chastening day for Sussex and a very good one for Northants.