Kettering were relegated from Blue Square Bet Premier after a 3-0 home defeat by Mansfield.
The Stags took the lead in the 14th minute when Lindon Meikle rose highest to head home Gary Roberts' cross.
Matt Green, who had earlier hit the woodwork, then fired home from Anthony Howell's assist.
Matt Rhead headed home Luke O'Neill's cross and the Poppies' misery was compounded when Ashley Westwood received a second yellow at the death.
VIEW FROM THE CHANGING ROOM
Kettering Town caretaker manager Ashley Westwood tells BBC Radio Northampton:
"We could've had a bit more luck [in the season] but we can't dwell on that. You've got to get your own house in order and we haven't done that.
"Relegation is bitterly disappointing. I've given it my all and it wasn't meant to be. It's not good on a CV, having a relegation, and we'll do our best to bounce back.
"In the time I've been here, we've been competitive and not got hammered in any game. You can take credit from that, but in the end, it wasn't good enough.
"The red card was embarrassing."
Mansfield Town manager Paul Cox told BBC Radio Nottingham:
"I don't think we were at our best in terms of the fluidity of our play but on a horrible, bobbly pitch we got the job done and that's all we came to do.
"I am just chuffed with the lads because there were a few tired legs out there and a bit of fatigue.
"I said at half time we had to be a bit more ruthless in front of goal and had to up the tempo. We also had to be patient and we knew we wouldn't have it all our own way but the lads worked extremely hard."