Three months after David De Gea's last-minute error sent Sunderland's supporters into delirium in the Capital One Cup semi-final at Old Trafford, Vito Mannone produced an equally unfathomable error at the Etihad Stadium that could well hasten the Black Cats' drop into the Championship.
With his side heading for a three-point haul that had the potential to transform their season, Mannone somehow allowed Samir Nasri's tame 89th-minute strike to squeeze through his grasp and trickle into the net.
It was a critical mistake from a player who has arguably been Sunderland's best player this season, and for all that there are five games remaining, it felt like the defining moment of a campaign that has lurched from one crisis to the next.
Instead of trailing by four points ahead of Saturday's trip to Chelsea, the Black Cats still find themselves six points adrift of safety. They can take plenty of positives from their spirited display against a City side who were equally deflated at the final whistle as their title hopes suffered what will almost certainly be a terminal blow, but it is points Sunderland need at the minute and they are rapidly running out of time to get them.
Trailing to Fernandinho's second-minute strike, the Wearsiders outplayed their illustrious opponents for large chunks of the game and looked like getting their reward when the hugely-impressive Connor Wickham claimed two goals in the space of ten minutes.
Had they held on to record a notable double over City, the momentum in the relegation battle would have been with them. As it is, Mannone's mistake felt like one deflation too many.
Repeat this performance in the final five games, and Sunderland could yet have a chance. Had they matched it in the recent games against Crystal Palace, Norwich and West Ham, however, the bulk of their survival work might already have been done.
At least, after weeks of increasingly desperate experimentation, Poyet appears to have found a system that works.
Santiago Vergini's recall in place of the suspended Phil Bardsley offered the Sunderland boss an opportunity to field another five-man backline, but the replacement defender played at right-back with Wes Brown partnering John O'Shea at the heart of a back four.
For the vast majority of the night, the visitors were defensively solid. One minute and 54 seconds in, however, and they were undone.
The opener featured a catalogue of failings from a Sunderland perspective, with Lee Cattermole the first player at fault as, not for the first time this season, he dawdled in possession, enabling Alvaro Negredo to steal the ball.
Negredo fed Sergio Aguero, and then dummied his team-mate's through ball, an act that effectively took two Sunderland defenders out of the game.
Fernandinho found himself in acres of space as he sprinted between Brown and Marcos Alonso, and while he might not be renowned as a goalscorer, the Brazilian calmly slotted a crisp strike past Mannone.
Sunderland have become adept at shooting themselves in the foot in recent weeks, but even by their own desultory standards, the concession of a goal inside the opening two minutes was a new low.
By rights, it should have sparked a wholesale collapse, and perhaps it would have done had Fernandinho not blazed over after Mannone could only parry Aguero's long-range shot.
As it was though, instead of falling apart, Sunderland regrouped to dominate the opening quarter of the game.
They carved out three good chances inside the opening 20 minutes, but crucially, found the target with none of them. In the final reckoning, a lack of composure in front of goal will have played a pivotal role in the Black Cats' anticipated demise.
Given that John O'Shea has only scored three times in his entire Sunderland career (in the right net), the visitors would not have chosen the centre-half to convert the first two opportunities of the night, and true to form, he failed to trouble Joe Hart with headers from an Adam Johnson free-kick and a Seb Larsson corner. Neither header was from more than eight yards out; neither even looked like dipping under the crossbar.
Fabio Borini tends to be more clinical in front of goal, but when the Italian was presented with an inviting opportunity inside the box in the 18th minute, he dragged a tame shot across the face of goal. It was a similar opportunity to the one he converted against City at Wembley, but the outcome was markedly different.
At least Sunderland were creating chances though, and with Johnson clearly relishing the opportunity to prove a few points on the ground he used to call home, Martin Demichelis' lack of mobility was repeatedly exposed. With Cattermole patrolling effectively at the base of midfield and Wickham battling gamely to hold on to possession in attack, Sunderland were the more potent team before the interval.
Given that their title prospects depended on a victory, Manchester City were surprisingly lacklustre throughout. Aguero, patently short of match fitness, played in fits and starts, and was replaced before the hour mark. His strike partner Negredo was equally ineffective, and looks a shadow of the player that was ripping Premier League defences apart before Christmas.
With the home crowd becoming increasingly subdued, Poyet's introduction of Emanuele Giaccherini and Ignacio Scocco reflected a belief that an equaliser was there for the taking, and it duly arrived with 17 minutes left.
Giaccherini, little more than a fringe player in recent weeks, was the architect, sprinting outside Pablo Zabaleta and standing up an inviting cross from the left. Wickham found himself completely unmarked after withdrawing to the back post, and volleyed home a crisp first-time finish.
Ten minutes later, and the England Under-21 international was at it again. Again Giaccherini was the supplier, releasing Wickham into the area in the inside-right channel.
There was a lot more to do this time, but Wickham was up to the task, drilling a fantastic low strike past Joe Hart's left hand.
With seven minutes remaining, Sunderland just had to hold on. City tried to build up a head of steam, but they looked to have run out of ideas before Mannone gave them a hugely significant helping hand.
Nasri's shot from close to the penalty spot lacked power, but Mannone somehow allowed it to slip from his grasp. Judging by the goalkeeper's crestfallen reaction, even he was instantly aware of just how crucial a moment it could be.