Dartford have been relegated from Skrill Premer after losing at home to Tamworth on Easter Monday.
Tony Burman's side needed a win to have any realistic hope of staying in the division, and Elliot Bradbrook's first-half strike would have taken their survival bid to the final day of the season.
But straight after Lee Noble had missed a great chance to make it 2-0, the Lambs equalised through Jessy Reindorf.
And when Kevin Thornton scored from the penalty spot, the Darts looked a beaten side.
Thornton's second goal at the death sealed their fate and although Bradbrook pulled one back in stoppage-time, it was far too little, too late.
The final whistle condemned them to the drop after two seasons in non-league's top flight.
There were two significant changes to the Dartford team which lost 1-0 at Braintree on Good Friday. Mikel Suarez, the only recognised centre-forward in the Darts squad, was dropped to the bench, while Nathan Collier also lost his place. Ben Swallow was recalled and despite not being fully fit, Bradbrook started.
Tamworth's team included Jack Evans, the former Gills player who had a loan spell at Dartford last season.
The home side went on the attack straight away. Swallow's clever back-heel gave Lee Burns room to deliver a deep cross from the right and Noble, who jumped well at the far post, headed it wide.
Bradbrook then delivered a fine diagonal pass into the feet of Jim Stevenson, whose goalbound volley was well blocked.
That start lifted the home crowd, although there was a nervous hush around the ground every time Tamworth were in possession. Reindorf nodded a deep cross wide and Thornton's shot skimmed just past the post after taking the slightest deflection off Bradbrook.
Back came the Darts, though, with Bradbrook stinging goalkeeper Cameron Belford's palms after collecting a pass from Noble inside the box.
When Alan Julian's long kick forward was flicked on by Bradbrook, Noble won the next header and latched onto the flick-on himself, with a Lambs defender getting in the way to block his strike.
Dartford lost Mat Mitchel-King to injury midway through the first half, Kenny Clark taking his place.
Swallow's volleyed pass picked out Bradbrook on the run moments later but the skipper couldn't keep his shot down.
Then came a big moment. Swallow's cross was nodded down by Bradbrook for Max Cornhill and he set up Noble for a shot which was blocked by Ben Richards-Everton. The home crowd howled for handball but referee Craig Hicks waved away their penalty appeals and pointed instead for a corner.
Dartford felt hard done-by but they'd forgotten the perceived injustice seconds later. Noble's corner dropped in the six-yard box and Bradbrook turned it home from close-range.
The visitors did threaten to restore parity before the half-time interval. Jake Caprice's long-range shot deflected wide and Thornton then went close, before Danny Harris turned Burns' cross wide of the near post at the other end.
Tamworth should have been level within 30 seconds of the restart. Dartford were sleeping when a free-kick dropped in the centre of their penalty area and Jordan Keane, unmarked, dragged his shot wide.
The home side weren't switched on at all. Rory McAuley had to hurl himself in front of a Lloyd Kerry shot which looked destined for the top corner, before Richard Peniket, arriving late and totally unmarked, nodded Claudiu Hoban's deep cross wide. And then another Thornton effort forced Tyrone Sterling to make an important block.
But Dartford should have doubled their lead soon after. Swallow made room on the left and swung over a great cross which picked out Noble in space at the far post. He had time to take a touch, but his shot was straight at Belford.
And that miss was punished emphatically from Tamworth's next attack, on the hour mark. A left-wing cross found Reindorf alone in the six-yard box and he planted the ball beyond Julian.
That might have taken the wind out of Dartford's sails but they had two good chances to re-take the lead. Bradbrook's pass to Harris set up a two-on-one break in the home side's favour but Harris couldn't make the most of it. The same player was involved moments later, lifting a lob over Belford but onto the roof of the net.
Burman threw on Suarez for Stevenson as the home side became more and more desperate. Centre-half McAuley tried his luck from 30 yards but the ball flew well wide.
At the other end, Kerry lifted a shot over with Julian beaten.
Then, with 12 minutes left, came the death knell. Kaiyne Woolery, formerly of Maidstone United, was clumsily shoved over in the box and Thornton beat Julian from the penalty spot.
That goal completely knocked the stuffing out of Dartford, who now looked a beaten side. Reindorf had a shot pushed round the post and Julian then saved from Kerry as the men in blue shirts finished the game in complete command.
It was no surprise when Thornton led an 89th-minute breakaway to slide the ball under Julian, ending any lingering hopes the Darts had of a dramatic comeback.
Bradbrook scored in the third minute of added time but it was no consolation.
Dartford: Julian, Burns, Mitchel-King (Clark 26mins), McAuley, Sterling (Woodyard 90mins), Swallow, Cornhill, Stevenson (Suarez 68mins), Bradbrook, Noble, Harris. Subs not used: Collier, Holloway.
Tamworth: C Belford, Evans, Hoban, Reindorf, Richards-Everton, Kerry (Baker 90mins), Thornton, Caprice, Peniket, Woolery, Keane. Subs not used: Byfield, Vanderhyde, Batis-Cande, D Belford.