Sussex 118 (Sanderson 4-32) and 4 for 0 trail Northamptonshire 171 (Robinson 4-55) by 49 runs
Ben Sanderson took four wickets and slugged a merry 36 from No. 11 to put Northamptonshire on top against Sussex after a first day's play where 20 wickets fell at Wantage Road.
After surprisingly contesting the toss and choosing to bat first, Sussex were bundled out for just 118 - Sanderson taking 4 for 32 - and then from 111 for 9, Northants were able to reach 171 all out and a very useful advantage thanks to some entertaining tail-end batting.
The ball swung and there was some inevitable help from a September wicket but it was by no means a pitch that should have delivered two complete innings within a day. Both sides bowled well and both sides, after good starts, failed to show any determination to occupy the crease.
Sanderson's first act of the day was to hurry Sussex out for a paltry total as they slid away from 58 for 1 after the ball was changed. He struck twice in two balls just before lunch - nipping one back to beat Laurie Evans' drive to remove his off stump for a smartly compiled 34, before Delray Rawlings edged his first ball to Ricardo Vasconcelos at slip. After lunch, Sanderson received an easy return catch from a Ben Brown leading edge before trapping Ollie Robinson lbw.
He gained plenty of support from Brett Hutton, whose 3 for 41 saw him pass 150 first-class wickets, and Ben Cotton - who produced the most eye-catching of the wicket with a delivery that jagged back markedly off the seam to take out Luke Wells' off stump.
With only 118 to bowl at, Sussex gained a perfect start when Vasconcelos edged to second slip for a five-ball duck but at 63 for 1, the home side looked set to take control of the game. However, again the ball was changed and again wickets started to fall.
Ben Curran, who went smartly to 36, flicked at Abidine Sakande - playing his first match of the season - and was taken by a retreating extra-cover before Charlie Thurston, 29 in his second first-class match, lost his off stump to one that moved away.
There followed a succession of very poor shots as Alex Wakely, Luke Procter, Adam Rossington and Rob Keogh all flirted outside their off stumps and were all caught via edges by either Brown the wicketkeeper or Harry Finch at second slip.
But just as Northants were about to be rolled over, Sanderson cracked six boundaries and a straight six off Sakande - fitting on such a barmy day. He and Cotton, who made an unbeaten 24 with three fours of his own, added 60 for the tenth wicket to give Northants a useful advantage of 53.
Sent in again for five overs before the close, Sussex survived 4 for 0.