Derby-day spoils went to Southwell after they produced a resilient performance to defeat Newark in a fiercely contested clash at Kelham Road.
Southwell made an excellent start, and held on in a thrilling finale to pick up a vital victory in the Midlands Division Two East (North).
A fourth defeat in five matches for Newark means their play-off aspirations have all but evaporated with four games left.
On a wet pitch, Southwell started brightly and took the early initiative through a Paul Rich penalty.
They increased their lead through Aaron Whittaker, who made a dash down the touchline to beat the Newark cover, with Rich adding the conversion.
Newark enjoyed their best period of the match before half-time and took advantage of a yellow card for Dan Montagu to hit back through two tries in quick succession.
Winger Alex Henderson and full-back Robbie Hunter-Shaw both went over before the break to give them a half-time advantage.
The home team continued on the front foot at the start of the second half but were unable to add to their lead.
Southwell took the initiative again midway through the half when Jack Skill intercepted a Newark move in midfield and then had the pace to race 60metres for a try, which was converted by Rich.
A further penalty, after the visitors were held up on the Newark line, stretched the lead to 20-12.
Southwell dropped the kick-off after the penalty, which spurred Newark on as they pressed for another response.
They staged a last-ditch rally, which brought a try for Dave Garland who finished off a forward drive.
However, the conversion went wide and another final attack broke down giving Southwell the opportunity to clear to end the contest.
Newark travel to Nottingham Casuals on Saturday while Southwell are due to play their re-arranged match at Coalville.
Southwell 2nds 21 Newark 2nds 41
A strong performance helped Newark 2nds to victory at Southwell 2nds in their Pennant fixture.
Alex Scott scored the opener for the visitors, but Southwell hit back with a prolonged period of pressure.
Tom Broughton scored twice in quick succession, one from an interception, as they took a 14-5 lead. He converted both scores.
Newark moved the ball around with purpose and went back into the lead before the break with converted tries by Jason Matthysz and Ali Moss.
They continued to put pressure on after the break with Moss, Harry Jenkins and Josh Seabrooke scoring within the first 20 minutes.
Southwell remained combative and pulled one back through James Beaumont, with Jake Crone adding a conversion.
However, Newark had the final say when Callum Sherriff scored on the right after a kick through from Scott.