Rory Kleinveldt led the Northamptonshire fight back, after Luke Wood had seemingly given Nottinghamshire the upper hand as they searched for the win that will seal promotion at Wantage Road.
Northants began the day 29 points adrift with two rounds to play but, after choosing to bowl first, Notts took control of the contest as they bowled the hosts out for 194, crucially denying them any batting bonus points.
Having top scored with 43, Kleinveldt then took four wickets as Nottinghamshire lost their top five before the close, Nathan Buck with the fifth as they were reduced to 80-5 still 114 runs behind.
Nottinghamshire knew a win this week would be enough to secure themselves, and Worcestershire, a return to the top flight and, whilst they might have been putting the champagne on ice after an impressive bowling display, they were given something to think about.
Northants’ lack of batting points mean a draw will be enough for the top two. That looks unlikely, however, unless the weather intervenes after a first day that saw 14 wickets fall on a pitch that offered assistance but was neither a green top or a minefield.
Wood removed openers Ben Duckett and Rob Newton early, and the hosts slipped to 120-7 before Kleinveldt and Buck dragged them to the verge of 200, Brett Hutton adding three wickets.
Newton had hit twin half centuries at Cardiff last week but only lasted 10 balls in the morning, trapped LBW to a traditional left armer’s dismissal from Wood, and in the fourth over Duckett got a leading edge to give Wood a return catch.
The hosts were 35-3 when Alex Wakely edged Brett Hutton into the slips and, whilst Richard Levi hit seven boundaries in his 30 ball 35 including three in one Wood over, he then played around one that swung back to go LBW.
Steven Mullaney then combined with Hutton to remove Rob Keogh and David Murphy, both caught at slip. The first was spectacular from Mullaney: one handed diving to his first, the second a more regulation chance.
Josh Cobb never looked settled before edging Harry Gurney into the cordon for 36, but Kleinveldt and Buck showed some resistance in a stand of 44, the highest of the day. Kleinveldt proved slightly restrained, whilst Buck began quietly before expanding his range of shots.
The former hit six fours in making 43, the closest anyone got to 50 in the opening day, before inside edging a drive off Samit Patel, who then had Sanderson caught at slip before Buck was last man out – Wood removing his off stump only after Buck had posted 32, his second highest FC score.
Northants began the evening knowing they needed wickets to maintain their promotion hopes, but were initially blunted by Steven Mullaney and Jake Libby, who scored 14 runs in 10 overs before Kleinveldt beat the former’s outside edge to disturb the stumps.
Three balls later Chetan Pujara edged into the slips before Libby, returning to the club he enjoyed a successful loan spell with at the start of last summer, was LBW.
Rikki Wessels had some early luck, whilst Samit Patel survived a huge caught-behind appeal off Ben Sanderson. He would depart the next over, though, trapped in front by Buck to make 56-4.
Wessels and Billy Root looked set to guide the visitors to the close, but ten balls before stumps Wessels had a lazy drive to Kleinveldt, bowling his 12th over of the session. He edged behind to give the hosts the initiative, with Notts hopes resting on the inexperienced pair of Billy Root and Tom Moores.