The result added to recent poor displays against West Brom, Newcastle and Crystal Palace, and now rumours of changing-room unrest have begun to emerge, with Eden Hazard and Ashley Cole alleged to be at their core.
The Daily Mail's Neil Ashton touches upon some of the issues at Stamford Bridge, which don't exactly echo the bond Jose Mourinho had with his players during his first reign at Stamford Bridge.
At the Chelsea training ground, Mourinho has outstanding issues with some players.
For one, Eden Hazard is first off the training pitches and first to get away after lunch. There is disbelief that a player with so much ability should choose to lead his professional life this way. He could be one of the best.
Mourinho insists there are no problems but there is a feeling Cole has had a raw deal. Although Cole started at Sunderland, he has fallen out of favour with Mourinho and it is a long way back from here.
Tuesday's trip to the Stadium of Light was Cole's first game in English competition since the 2-0 defeat to Newcastle United on Nov. 2, his outing against Steaua Bucharest last week being the only other run-out the veteran has received in recent months.
Instead, Mourinho has opted to utilise the right-footed Cesar Azpilicueta in the left-back spot which, despite the Spaniard's good form, has come as something of a strange decision.
However, word of Hazard's unrest will be all the more worrying for those at Stamford Bridge, considering how essential the Belgian international is considered to the club's cause.
OptaJoe shows just what the youngster brings to Mourinho's side:
Juan Mata's exclusion has already been an unexpected product of Mourinho's return to the club, the Spaniard recently starting four Premier league games in a row for the first time this season.
However, the two-time Chelsea Player of the Year is still yet to score this term, such has been the disruption compared to previous campaigns.
TalkSPORT's Adrian Durham clearly feels Cole still has something to offer his side:
Cole's contract is once again set to expire this summer, but his manager recently told BBC Sport there are no concerns over the expiring deals of the Blues' longest servants.
Mourinho might be wise to place a priority on convincing 22-year-old Hazard that all is well in West London. The young winger has been a sensation since signing from Lille last summer and has another three-and-a-half years left to run on his current deal.
Currently two points away from Premier League leaders Arsenal and through to the knockout stages of the Champions League, things certainly aren't all bad at Chelsea right now.
With such an expensively assembled squad, however, the last thing the club would like to see emerge as their undoing is themselves.