The second post-Jose Mourinho era will begin on Saturday afternoon when Chelsea host Sunderland at Stamford Bridge.
Just three points separate the two struggling sides in the Premier League table, and defeat could leave either in the relegation zone on Christmas Day.
Chelsea
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The writing had been on the wall for some time, but it still came as something of a surprise when Mourinho's second reign at Chelsea was brought to an end on Thursday. Just seven months previously, the self-proclaimed Special One was guiding the club back to the top of English football after five years of playing second fiddle to a Manchester monopoly.
Quite what has gone wrong since then is up for debate, although the short answer is everything. Mourinho has always been accompanied by a circus, but the off-field troubles this season have been more damaging than ever before.
That they have come in the midst of such struggles on the field has only highlighted them further, and it is fair to say that Mourinho failed to adequately cope with what was the first really sticky patch of his illustrious career.
In the end, the Portuguese was afforded more time than others would have been in a similar scenario. He remains the club's greatest ever manager having steered them to three of the five league titles that they have ever won, and even if he never works again, Mourinho will be regarded as one of the greatest coaches in football history.
There is no getting away from just how dire this season has been, though. The Blues have so far put in the worst title defence that the Premier League has ever seen and their own worst start to a season since 1978 - a campaign that ended in relegation.
A battle to avoid the drop this season still seems unthinkable despite only one point separating them from the relegation zone approaching the halfway stage of the campaign, but anything other than maximum points from consecutive home games against Sunderland and Watford either side of Christmas would pile even more pressure on Mourinho's successor.
The likes of Guus Hiddink, Juande Ramos and even Brendan Rodgers have been linked with the post on a temporary basis before the big boys - Pep Guardiola, Carlo Ancelotti and Diego Simeone - may become available in the summer. Hiddink is the heavy favourite at the moment, having previously led Chelsea to FA Cup success in 2009.
Whoever gets the job will have a big ask to salvage anything from the season, but on the plus side things can surely only get better. The form of Eden Hazard, the reigning PFA and FWA Player of the Year who is yet to score a single goal this term, is perhaps the perfect microcosm of Chelsea's campaign so far.
Monday night's 2-1 defeat to Leicester City not only made it just one win in their last seven league games and nine defeats in 16 outings, but it also showcased one of the major problems with Chelsea so far this season. Hard work will always beat talent if talent isn't working hard.
There is likely to be a reaction this weekend, but defeat would see them fall to three consecutive league losses for the second time in as many months having not been beaten three times on the bounce since 1999 before this season.
More than that, though, it would leave them in a very precarious position at Christmas and, with teams around them beginning to pick up points, Chelsea need to follow suit if they are to avoid being dragged into a genuine relegation battle.
Recent form: LLWDLL
Recent form (all competitions): WWDLWL
Sunderland
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If, during the summer, you had offered Sunderland the chance to be able to move level on points with Chelsea at Christmas, they would have snapped your hand off.
They would not have imagined making the trip to Stamford Bridge in quite these circumstances, however. Chelsea's slide has been more dramatic than anyone could have expected, but Sunderland's own plight has been far more predictable.
As is becoming the custom at the club, there was managerial change early in the campaign when Dick Advocaat left having helped them to avoid relegation at the end of last season, and the latest man to be charged with that task this time around is Sam Allardyce.
There has certainly been an improvement during his time at the helm. No longer does Sunderland's defending come under the 'comical' category and, a 6-2 defeat to Everton aside, rarely are the Black Cats soundly beaten anymore.
Even so, five defeats from eight matches is the sort of form that will keep them down at the wrong end of the table, and there aren't too many signs of that improving over the festive period - Chelsea, Manchester City and Liverpool are their final three opponents of 2015.
Any points from that triple-header would be a bonus, although they may see this weekend's game as a good chance to take advantage of a Chelsea side in disarray. Victory could be enough to lift them out of the bottom three, and they have previous on this ground having inflicted Mourinho's only home league defeat in his first 99 Stamford Bridge outings.
Chelsea have lost four of their last seven in front of their own fans too, while Sunderland actually come into the game in better form than their opponents - they have picked up 10 points to Chelsea's seven since the start of October.
However, the Black Cats do have the worst away record in the league this season, while in 2015 they have won just two of their 18 top-flight matches on the road.
Recent form: LLWWLL
Team News
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Chelsea will hope to have Hazard fit and available this weekend despite the Belgian limping off during the defeat to Leicester on Monday night.
The winger will undergo a late fitness test, but could be replaced by Pedro in the starting lineup should he not be deemed ready to play.
Radamel Falcao is the only other fitness doubt for the Blues, but the departure of Mourinho could pave the way for Cesc Fabregas to return to the side having been left on the bench in recent weeks.
Sunderland, meanwhile, should be able to recall Younes Kaboul after he missed the defeat to Watford last weekend, while Sebastian Coates is also expected to overcome an illness to play.
Jermain Defoe will be hoping for a recall to the starting XI, but Sebastian Larsson and Lee Cattermole are both still sidelined and will play no part.
Chelsea possible starting lineup:
Courtois; Ivanovic, Zouma, Terry, Azpilicueta; Fabregas, Matic, Willian, Oscar, Hazard; Costa
Sunderland possible starting lineup:
Pantilimon; Coates, O'Shea, Kaboul; Yedlin, M'Vila, Toivonen, Van Aanholt; Borini, Defoe, Watmore
Head To Head
Chelsea have generally dominated the recent meetings between these two sides, winning 18 and losing just two of their last 21 Premier League clashes.
The corresponding fixture last term saw Chelsea come from behind to pick up a 3-1 victory, with Diego Costa and Loic Remy (2) cancelling out Steven Fletcher's opener.
Sunderland did hold the champions-to-be to a goalless draw at the Stadium of Light last November, however, while before May's defeat in West London the Black Cats had gone three games without losing to Chelsea in all competitions.
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Hit play below to see what the Sports Mole Sofa had to say about this encounter:
We say: Chelsea 2-0 Sunderland
Expect a reaction from the Chelsea players following what has been a seismic few days for the club. They have quality, of course, and a change is perhaps all they needed to get firing once again. Mourinho's departure could be that change, and Sunderland may find themselves in the wrong place at the wrong time here.
Barney Corkhill
