Orient looked destined for the Championship when the half-time whistle blew in Sunday's League 1 play-off final against Rotherham at Wembley, but their opponents came back from two goals down to set up extra time and eventually win on penalties.
Moses Odubajo hit a wonderful left-footed volley on 34 minutes before setting up Dean Cox to tap in at the far post before the break, sending more than 24,000 O's fans into raptures and giving them a formidable 2-0 lead at half-time.
Orient scored both their goals in a five minute period, stunning the Millers, but it was a complete role reversal in the second half when Rotherham's Alex Revell - formerly of Orient - struck twice in a five minute window to miraculously level the tie by the hour-mark.
After suffering such a killer blow, the O's showed tremendous character to ensure they did not let their heads go and regained a certain amount of control when they could easily have collapsed under the tidal wave of momentum Rotherham possessed after equalising.
The remaining half an hour of normal time was evenly balanced and it was the same story during an agonising 30 minutes of extra time for both sets of fans and players. The O's looked to be on their way to victory once more after making a great start to the penalty shoot-out but, in a final twist, Rotherham came back from behind again thanks to two heroic penalty saves from goalkeeper Adam Collin.
There was nothing to choose between the two sides coming into the match so it should be no surprise that the game was so closely contested. Both ended the regular season on 86 points and each had taken three points off the other in the two league fixtures earlier in the campaign, with both those matches being decided by just a single goal.
The Orient backroom staff and players made every effort to treat this game like any other, realising the importance of sticking to the routines that have served them so well all season. And the impetus on continuity was demonstrated through Russell Slade's team selection for the Wembley tie.
The O's starting XI was not only the same as the one that stormed to victory against Peterborough in the second leg of the play-off semi-final, but also the one Slade had named most regularly throughout a season of remarkable success. Meanwhile Rotherham boss Steve Evans also sent out an unchanged team after beating Preston 3-1 in the decisive leg of their semi-final with Preston a week-and-a-half ago.
But, however familiar the names on the teamsheet and pre-match preparations were for both teams, this was a game of unprecedented magnitude in surroundings that were alien to the majority of men on the field.
The Wembley crowd was a sea of red and white but it was Orient who were given the privilege of wearing their home strip on the day as they finished the season in the higher league position, while the Millers lined up in all grey.
Rotherham, through the left boot of Ben Pringle, are renowned for the threat they pose at set pieces and Orient will have been pleased to come through an opening spell which included a couple of free-kicks in dangerous positions without conceding, however Slade will have been keen for his side to prevent any further fouls being given away.
Cox, whose brilliantly controlled volley set the O's on their way to the win over Peterborough, was again looking lively and it was his cross from the left which presented Orient with their first chance of the afternoon but Odubajo fired over from an difficult angle at the back post.
Each side deployed a 4-4-2 formation, seeing them cancel each other out in the middle of the park, with both being forced into playing a direct style of football - something the Millers are more accustomed to than Orient - but it was the O's who were causing more problems in the final third despite a couple of tame long-range efforts from Rotherham duo Lee Frecklington and James Tavernier.
Orient's front four were winning the majority of first and second balls in and around the Rotherham 18-yard box and, when the ball fell at the feet of David Mooney shortly before the half-hour mark, the Irishman had a snap-shot that a good number of the Orient fans - who were located in the stand behind their own goal in the first half - thought had gone in only to realise it had struck the side-netting.
And it was Orient's ability and hunger to get to the loose balls that led to them taking the lead on 34 minutes. First, Lisbie used every ounce of experience he's gained throughout his long and successful career to win a free-kick wide on the left. The resulting delivery in to the box was only cleared to the edge of the area where Odubajo was lurking and the winger chested down the ball before lashing home from 20 yards with his weaker foot.
Earlier in the week, Odubajo had won the the Football League's Young Player of the Month award in recognition of his impressive finish to the season, including the crucial equalising goal in the first leg of the play-off semi-final with Posh, and this latest strike proves what a huge talent he is.
And just five minutes later, Orient found themselves two goals ahead.
Mooney attempted to flick the ball over the head of a Rotherham defender Craig Morgan which would have put him through on goal but Tavernier got across to cover and the ball was deflected into the path of Odubajo who remained composed enough to square it across the face of goal for his opposite winger Cox to score one of his simplest of the season.
Orient did a good job of keeping hold of possession after Cox doubled their lead but were given a scare when Pringle fired a volley goalwards in first half stoppage time. The ball dipped and swerved before landing on the roof of Jamie Jones's net, much to the relief of everyone in the O's end.
Not willing to come out and simply protect their lead in the second half, Orient made a lively and attacking start after the break however two clumsy tackles on the edge of their own penalty area allowed Rotherham to go close with two set-pieces early on.
The O's may have escaped twice but a third free-kick that was conceded wide on Orient's left proved one too many and this time the Millers were found the net. Jones came out and failed to make contact with Tavernier's delivery and the ball ricocheted into the path of Revell who stabbed home into an empty net.
Rotherham sensed that they could claw their way back into a game which looked to be beyond at half-time, and Revell hit his former team with a sucker punch just five minutes after notching his first.
The striker was 35 yards out when he picked up Kieran Agard's knock-down and struck an unstoppable looping volley up and over Jones, who had little chance despite the distance it was hit from.
Orient reacted admirably to a situation which could have seen them collapse under the shock of letting a two-goal lead slip and began to regain control, looking as dangerous as ever on the counter-attack.
Shaun Batt and Chris Dagnall, who both had a huge impact from the subs bench against Peterborough, were introduced as the game entered the last 15 minutes and the pair unsettled the Rotherham back four straight away.
Orient were really probing as the final whistle drew closer and Rotherham spent much of it camped inside their defensive third. However it was proving hard to find the decisive pass and the Millers remained a threat on the break.
Agard's pace allowed him to escape the O's back four with eight minutes left but Rotherham's top scorer blasted his left-footed shot high and wide of the O's goal. Two crosses from either flank were also met by the head of the Millers striker in the final minutes but he again failed to direct his efforts on target.
During five minutes of time added on, Orient forced three corners back-to-back, but there was to be no last-minute winner as there was in the Championship play-off final the day before.
Orient almost suffered heartbreak within minutes of extra time starting when Scott Cuthbert headed a Rotherham cross towards his own goal but Jones was incredibly alert and made a stunning one-handed save to send the ball behind for a corner. From the resulting corner, Orient hit their opponents with a blistering counter-attack which ended in Mooney sending a delicate chip inches over the bar.
The game could not have been more finely balanced and neither team looked prepared to wait for penalties, playing with the same intensity and ambition as they had done throughout the first 90 minutes of the match.
Batt continued to be a thorn in the side of the Millers defence and did well to draw a foul on the byline shortly before half-time but skipper Nathan Clarke couldn't quite direct his header on target from James's delivery.
And, just the other side of the break, Dagnall was the one who almost benefited from good work by Batt. The rangey striker threaded a great pass through to Dagnall but he couldn't get the ball out of his feet to produce a shot when in a great position, allowing the Rotherham defence the chance to recover and clear the danger.
Orient finished much the stronger but despite throwing everything into the Rotherham box in the final stages could not find a way past the Millers rearguard, meaning the fate of the two sides who now looked exhausted would be decided on penalties.
O's captain Clarke won the coin toss and chose for the penalties to be taken in front of the Orient faithful and they got off to a great start - James, Lundstram and Clarke held their nerve brilliantly while Jones saved from Frecklington.
However the Millers scored all their remaining kicks while keeper Collin saved Orient's final two from Mathieu Baudry and Chris Dagnall, ultimately winning the game and securing promotion to the Championship for the South Yorkshire side.
It was the cruelest way for Orient's season to end but the achievements of Russell Slade and his squad this campaign cannot be underestimated.
ORIENT: Jones, Cuthbert, Baudry, Clarke (C), Omozusi, Odubajo, James, Vincelot, Cox (Batt, 74), Mooney (Lundstram, 106 [ET]), Lisbie (Dagnall, 76)
SUBS NOT USED: Larkins, Sawyer, Bartley, Simpson
GOALS: Odubajo (34), Cox (39)
BOOKINGS: Cuthbert (31), Odubajo (34), Clarke (64), Mooney (94 [ET])
ROTHERHAM: Collin, Tavernier, Morgan, Arnason, Skarz (Milsom, 77), Agard, Smallwood, Frecklington, Pringle, Revell (Vuckic, 105 [ET]), Thomas (Brindley, 54)
SUBS NOT USED: Shearer, Davis, O'Connor, Hitchcock
GOALS: Revell (55), (60)
BOOKINGS: Morgan (34), Tavernier (77), Pringle (87)
REFEREE: David Coote