Victor Moses came off the bench to score an incredible last-gasp winner as Chelsea somehow survived a Shakhtar Donetsk onslaught to keep their Champions League fate in their own hands.
The Blues were in danger of being the first holders to crash out of the competition before Christmas as former target Willian twice cancelled out almighty howlers from goalkeeper Andriy Pyatov which gifted goals to Fernando Torres and Oscar, the latter's fourth in as many Champions League games.
But late substitute Moses nodded home Mata's 94th minute corner to steal a barely-believable victory that put Chelsea level on points with their opponents at the top of Group E with two games remaining.
Blues boss Roberto Di Matteo refused to shy away from the importance of tonight's game from the moment the final whistle went in the reverse fixture - which Chelsea lost two weeks ago - branding it must-win.
As if to drive home the point to his players, the following fortnight saw him dub the match Chelsea's biggest since the May's final and claim his side needed to produce a "perfect" performance to succeed.
That made his decision to leave John Terry on the bench - albeit for match-fitness reasons - a massive gamble, with the holders having shipped 10 goals in the four games their captain had missed during his domestic racism ban.
The Blues were also without Ashley Cole against a team who had not lost for almost 12 months and had won an astonishing 19 of their 20 matches this term.
That included the reverse fixture, in which Shakhtar never looked back after racing into an early lead.
But they saw the tables turned tonight thanks to Pyatov, whose attempted clearance from Yaroslav Rakitskiy's backpass was closed down by Torres and careered into the net.
The visitors should have equalised when Luiz Adriano produced an airshot but they were level in the ninth minute when Willian fired home Fernandinho's cutback after a crucial slip by Ryan Bertrand.
Cole's understudy, playing his biggest match since the Champions League final, was having an absolute nightmare, making a succession of basic errors that threatened to cost Chelsea.
Petr Cech prevented him diverting a corner into his own net before making an acrobatic save from Fernandinho's long-ranger.
At least Torres was looking more interested than he had in the defeat in Donetsk.
He twice went close to nodding in brilliant Branislav Ivanovic crosses but, otherwise, Shakhtar were in complete control, popping the ball about as if they were the home side.
A breathtaking one-touch move almost saw them take the lead in the 32nd minute when Alex Teixeira shaved the post from 18 yards.
Chelsea fans began calling for Terry but they were soon celebrating their side going ahead completely against the run of play thanks to the madness of Pyatov and genius of Oscar.
Pyatov came charging out to head Juan Mata's harmless 40th-minute cross clear but the ball fell straight to Oscar, who produced a sublime 40-yard half-volley that sailed over the goalkeeper and into the net.
Eden Hazard also forced a good fingertip save from the beleaguered stopper before a frenetic half was out.
Stung by the injustice of being behind, Shakhtar took less than two minutes to equalise again after the restart with another stunning move, Fernandinho's defence-splitting pass and Darijo Srna's cross allowing Willian to stroke home.
Cech got away with a Pyatov-like clearance and Razvan Rat's first-time half-volley clattered the post from 25 yards out before Torres wasted a great chance to turn in Hazard's free-kick after Teixeira was booked for tripping the Belgian.
Pyatov almost gifted Oscar another clearance and Tomas Hubschman brought down Torres for a free-kick which John Obi Mikel powered home from Mata's cross.
But the midfielder was rightly denied his first goal for five years by an offside flag.
Chelsea, who were now on top, had genuine cause for complaint 16 minutes from time when a flying Ramires was convinced he had been bundled over in the box by Srna but referee Carlos Velasco Carballo was unmoved.
Teixeira was replaced by Ilsinho before Oscar was denied by a desperate Rat tackle and Mikel volleyed Pyatov's punch narrowly wide.
Moses came on for Oscar and Willian cleared Gary Cahill's dangerous header as Chelsea poured forward but they were almost caught out on the break, leading Luiz was booking late on and nearly a winner for Henrik Mkhitaryan.
But in the 94th minute, Chelsea won a corner which an unmarked Moses nodded in seconds before the final whistle.