Nottinghamshire 406 and 139 for 3 (Mullaney 59) lead Somerset 372 (Hildreth 161, Compton 87, Gurney 5-81) by 173
Nottinghamshire and Somerset continued to make the most of batsmen-friendly conditions after learning that their Division One status had already been preserved for another season.
Both sides would still have been vulnerable if Derbyshire had been able to win their final contest but as news filtered through of their defeat to Warwickshire, 17 miles away, attention returned to matters at Trent Bridge with a sixth-place finish up for grabs.
Somerset collected four batting bonus points after reaching 372 in their first innings, with James Hildreth eventually falling for 161 and Harry Gurney returning career-best figures of 5 for 81.
Beginning again, Nottinghamshire batted positively in advancing to 139 for 3, an overall lead of 173, with Steven Mullaney making a quickfire 59 for the hosts
Hildreth had earlier passed 1,000 first-class runs for the season during his stand of 248 with Nick Compton, who was eventually bowled by Samit Patel's quicker ball for 87. Gurney, who had removed Marcus Trescothick the previous evening, boosted his own tally of wickets after the second new ball had been taken.
Its first victim had been Hildreth, caught behind off Luke Fletcher - presenting Chris Read with his 750th catch for Nottinghamshire and a dismissal that heralded the start of three wickets falling in a seven-ball spell.
Jos Buttler was then trapped lbw by Gurney for 13 and left the field without any obvious farewell gestures, despite the rumours of an impending move, before the left-arm fast bowler also removed Craig Meschede. Lewis Gregory chanced his arm in making an undefeated 40 which included an uncontrolled pull for six off Brett Hutton, but then ran out of partners as the innings was wound up.
Peter Trego guided Gurney into the hands of point and the bowler's first Nottinghamshire five-wicket haul and his 100th first-class scalp was Alfonso Thomas, well caught at slip by Riki Wessels.
Mullaney set the tone for Nottinghamshire's second innings, racing to a half-century in just 38 balls, with 11 fours but then drove Trego to mid-off. Wessels and Michael Lumb each added 20 but the day had a slightly curious ending as Craig Kieswetter removed the wicketkeeper's pads to have a bowl but Trescothick - rather than Buttler - put them on for the final five overs.
With both sides locked together on exactly the same number of points - Somerset having won one game more this season - Nottinghamshire will need to force the win on the final day of the season to go ahead of their west country rivals.