Victor Moses came off the bench to score a dramatic last-gasp winner as Chelsea somehow survived a Shakhtar Donetsk onslaught to prevail 3-2 on Tuesday.
The Blues were in danger of being the first defending champions to crash out of the competition before Christmas as former target Willian twice canceled out blunders from goalkeeper Andriy Pyatov, who 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 an improbable win that put Chelsea level on points with their opponent at the top of Group E with two games remaining.
Blues boss Roberto Di Matteo refused to shy away from the importance of Tuesday's game from the moment the final whistle went in the reverse fixture -- which Chelsea lost two weeks ago -- branding it a must-win.
As if to drive home the point to his players, the following two weeks saw him dub the match Chelsea's biggest since the May final and claim his side needed to produce a "perfect" performance to succeed.
That made his decision to leave John Terry on the bench a massive gamble, with the champion having ceded 10 goals in the four games the team 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 the Ukrainians saw the tables turned 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 equalized when Luiz Adriano produced an airshot but were level in the ninth minute when Willian fired home Fernandinho's cutback after a crucial slip by Ryan Bertrand.
Cole's backup, 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 dazzling one-touch move almost saw the visitors 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 equalize 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.