Ebbsfleet sunk Leyton Orient in front of more than 3,000 on a famous afternoon at Stonebridge Road.
The O's arrived top of the National League but were sent home empty-handed by goals from defenders Jack King and Chris Bush.
Goalkeeper Nathan Ashmore made a string of outstanding save but this was a team performance of the highest quality from Garry Hill's side.
Ebbsfleet, playing for the first time in two weeks, made just one change from the controversial draw at Chesterfield with Danny Kedwell returning up front alongside Michael Cheek.
It was a first half of few clear chances although Fleet created an excellent one in the 10th minute.
Andy Drury started the move, winning the ball with an excellent tackle on the edge of his own penalty area, and Ebou Adams then helped the ball in behind the O's defence. Cheek latched onto the pass and seemed to have rounded keeper Dean Brill but, on the stretch, couldn't steer the ball into an open goal.
Either side of that miss, Bagasan Graham forced Brill to push his low shot round the post after playing a smart one-two with Danny Kedwell, who then headed Bush's free-kick wide under pressure from a defender.
However, there was the unusual sight of an indirect free-kick inside the Fleet box at the other end after Nathan Ashmore picked up a back-pass. The keeper made amends, however, charging down Macauley Bonne's powerful shot after Jordan Maguire-Drew had rolled the ball into his path.
Brill flapped at a Jack Payne corner and the ball was almost forced over the line, although the referee had spotted a foul.
Fleet took the lead on 22 minutes and the goal came from an unlikely source. Orient failed to clear their lines from another corner, Bush helped the ball back into the box and King hooked a brilliant shot into the top corner despite Brill getting fingertips to his effort.
The visitors dominated possession after that but Fleet held their defensive shape well and dealt with several long throws from Sam Ling.
Maguire-Drew got the wrong side of Bush but dragged his low shot across the face of goal from six yards before Ashmore pulled off a quite stunning save.
James Brophy got away from Lawrie Wilson down the O's left and cut the ball back for Bonne, whose shot was destined for the top corner until Ashmore arched his back and somehow clawed it out.
Waves of Orient attack were repelled by a determined red wall in the latter stages of the first half and Ashmore spread himself well to thwart Bonne again - although the striker, latching onto a deflected shot from George Elokobi, was standing in an offside position.
Orient were straight on the front foot at the start of the second period, forcing a number of set-pieces, although Wilson almost sent Graham racing clear on the counter-attack. The game was on a knife-edge now and both sets of fans turned up the volume to create a brilliant atmosphere.
Payne had a shot well blocked from Graham's cutback but it was all hands to the pump for Ebbsfleet as the visitors poured forward.
More heroics from Ashmore denied first Josh Koroma and then Dan Happe, who looked certain to nod home Joe Widdowson's knockdown.
But the home side scored an outrageous second goal on 63 minutes when Bush bent a brilliant free-kick into the top corner from 25 yards with Brill grasping thin air.
Orient responded by making a triple substitution but Fleet remained stoic in defence, with Payne heading off the line and Drury throwing himself in front of an Alex Lawless shot on the edge of the box.
It was almost 3-0 when the outstanding Cheek got to the byline and squared for Kedwell, who stepped inside and blazed over.
Bonne skied a shot over from Brophy's low cross but the game was still in the balance and it needed a full-length dive from Ashmore to turn the ball against the post when Fleet failed to clear their lines from a high ball.
Koroma tried his luck with a late free-kick but Ashmore refused to be beaten, making yet another save.
Rance threw himself in front of a Lawless shot in stoppage-time and Wilson cleared off the line with virtually the last kick of the game.
They were moments which typified Fleet's relentless work ethic from start to finish and the men in red were rightly cheered from the field at the end of a heroic display.
Ebbsfleet: Ashmore, Wilson, Magri, King, Bush, Adams, Drury (Rance 83mins), Payne, Graham (Whitely 80mins), Cheek (McDonald 90mins), Kedwell. Subs not used: Weston, Miles.
Leyton Orient: Brill, Ling, Happe, Elokobi (Turley 66mins), Widdowson, Maguire-Drew (Harrold 66mins), Lee (Clay 66mins), Lawless, Brophy, Koroma, Bonne. Subs not used: Sargeant, Alabi.