Chelsea had been braced for the death of the slow-burning dream. They had come to consider Pep Guardiola, now Bayern Munich-bound and the ideal choice as their next permanent manager, as being beyond them. Instead the shock waves came from the latest home failure against a Southampton side that had looked finished as they trailed to fine first-half goals from Demba Ba and Eden Hazard.
Chelsea had won 87 of the 89 Premier League matches since 1992 in which they had been two goals to the good at the interval yet they surrendered here, as the Southampton manager, Nigel Adkins, made attacking changes and enjoyed almost implausible reward. After his first substitute, Rickie Lambert, had reduced the deficit, his team prolonged their recent encouraging sequence with a dramatic equaliser on the counter, which was smashed home in emphatic style by Jason Puncheon.
Rafael Benítez had bemoaned how visiting teams had frustrated Chelsea at this stadium by sitting deep and packing numbers behind the ball. Yet this was a twist to his burgeoning frustration. The Southampton left-back Luke Shaw was deep inside his own half when he began the surging run that led to Puncheon's late goal.
It was difficult to forgive the manner in which Chelsea caught a sucker punch when in control and the home crowd was in no mood to do so. They had responded badly to Benítez's decision to replace Frank Lampard with Fernando Torres in the 80th minute and, after the Spain striker, playing towards the right flank, had laboured and snatched at his one chance, the full-time whistle brought another round of boos, together with the reminder for Benítez that he is not wanted here.
This was the night when Chelsea were supposed to put daylight behind them in third place but the lowest home league crowd of the season departed with further fuel for their grievances. Benítez has overseen only two Stamford Bridge wins in seven games in all competitions.
Southampton created little but they were rewarded for their refusal to accept the seemingly inevitable and their determination to stick to their game plan, which involved only one up front, staying compact and not chasing the game when they trailed to leave themselves exposed. Adkins remarked that this had seen Aston Villa undone here by an 8-0 scoreline while he also had the experience of the 5-1 FA Cup defeat by Chelsea at St Mary's Stadium on the Saturday before last.
Even so, it was remarkable that Chelsea were unhinged by Shaw's burst and Puncheon's spectacular left-footed blast because their comfort had been marked for long spells. Lambert's goal, two minutes after his introduction, had been a dreadful one to concede and it felt as though Chelsea had been lulled into false security. Nathaniel Clyne looked to have been slide-tackled by Hazard, only for the Chelsea winger weakly to allow him to wrest back possession, maraud further forward and cross. Lambert dropped off Gary Cahill, César Azpilicueta froze and the striker craned his neck to head firmly beyond Petr Cech.
But Chelsea responded. Ba volleyed over from Juan Mata's dinked pass and Lampard sent a free-kick over the wall and wide. The next goal looked likelier to be Chelsea's, despite this being far from a vintage performance. And yet, when Puncheon took his touch to tee up the decisive moment and the crowd howled at full-time, Benítez found himself forced to lament his players' lack of know-how and game management, along with their lack of ruthlessness in front of goal.
The outpouring upon the final whistle contrasted with the apathy at the outset, when there had been little to stir the senses in the cold. Chelsea, though, got the breakthrough they wanted midway through the first half and it seemed for a while to have fortified them.
Benítez started with arguably his most exciting attacking midfielders but it was the selection of Ba in preference to Torres up front that appeared the vote-winner, given the boos that the latter had suffered here against Swansea City in the League Cup last Wednesday.
Ba marked his Chelsea debut after his £7m arrival from Newcastle United with two goals in the FA Cup drubbing of Southampton and he offered another glimpse of his clinical nature. Adkins was cursing his players' inability to clear adequately when Lampard showed skill on the right and Azpilicueta crossed with zip. Oscar flung himself into an attempted header, with Jos Hooiveld in close attendance, and the ball spun up towards Ba. In a flash he had leapt into a right-footed volley and squeezed it past Artur Boruc into the corner.
Chelsea finished the first half with panache. Twice Lampard went close and Hazard brought a reaction save out of Boruc before Chelsea took charge with another eye-catching strike. Southampton once again failed to clear and after Ramires's deflected shot had come back off a post Hazard guided home the rebound first time and left-footed. A home win looked assured. Chelsea's disbelief would be tangible.