A Ecen Hazrd wonder goal on the stroke of half-time salvaged a point for the Blues at Douthampton in a game they should have won after almost total dominance.
The significance of the loss of two points won't be measured fully until the end of the season, but if they prove to be pivotal, and Chelsea are overhauled at the top of the Premier League, then they will rue missed chances here but also concede that Southampton proved themselves to be gallent defenders of their six-yard box.
Jose Mourinho made three changes from the Boxing Day side that beat West Ham United 2-0 - Filipe Luis in for Cesar Azpilicueta, Mikel for Oscar and Andre Schurrle for Willian.
After a family sedate opening minutes, Chelsea started to crank up the gears forcing three quick corners, the second of which almost yielded dividends with John Terry inches away from a Cesc
Fabregas drive into the Southampton penalty area.
Southampton almost stole the lead on 13 minutes through their first corner, but Terry was on had at the far post to thwart Jose Fonte. This spurred the Saints on and, on 16 minutes, when Nemanja Matic was dispossessed in midfield, Gary Cahill had to produce a goal-saving interception, preventing Sengalise Sadio Mane, who had got free in the Chelsea area from latching onto the through-ball.
But he was Jonnie on the spot a minute later, beating the Chelsea offside trap to cooly chip the ball in Thiabout Courtois to open the scoring.
Chelsea responded by attempting to control possession and make inroad, down the left where Eden Hazard and Fabregas were getting into good attacking positions, but failing to provide the decisive ball to striker Diego Costa.
Matic, not having the best of games was handed a yellow card for a mistimed challenge in midfield by referee Anthony Taylor on 31 minutes.
Some brilliant last-gasp deafening from the Saints centre back pairing of Fonte and Toby Alderweireld halted Chelsea's attacks in the final third as the Blues regained control of the match, possession-wise.
From set-pieces and counter-attacks Southampton were at their most dangerous.
Deep into the three added minutes in the first half and, for once, Chelsea had a piece of luck going forward. Hazard found himself free on the left, and from a clipped ball by Fabregas, the Belgium midfielder cut in, cruised past two Saints defenders before planting the perfect, right-footed, curling daisy-cutter past Fraser Forster's outstretched left hand to plant the ball into the back of the net to level the scores.
Jose Mourinho decided to haul off Schurrle at half-time, replacing the German World Cup winner with Brazilian wide man Willian.
Two strikes on goal from Willian signalled his intent, but both were charade down.
Then incredibly Chelsea were denied a stonewall penalty as Fabregas was clipped by Saints debutant Matt Targett. To add insult to injury, referee Taylor played on and then stopped play to hand the felled Spain midfielder a yellow card for simulation.
Maya Yosida was then given a yellow for cynically hacking down Hazard as the game looked as if it was going to become fractious.
Ronald Koeman replaced Dusan Tadic with James Ward-Prowse on 58 minutes. The first action on goal after the restart almost saw the visitors take the lead when Hazard's trickery saw him create space to unleash a left-footer that zipped across Forster's goal. Willian and Costa were racing in but the ball was just a tad to pacy and inched past the far post for a goal kick.
The next replacement saw Koeman take off yellow-carded Yosida for Florin Gardos on 62 minutes.
Southampton's ability to defend their six-yard like Trojans prevented Chelsea from making much headway their dominance of possession afforded them.
With 18 minutes on the clock, Morgan Schneiderlin was given a yellow card for hauling down Hazard.
Jose Mourinho, determined to go all out for victory had two strikers in the bench, just in case, and, on 74 minutes, opted to double his attacking force at the expense of a holding midfielder. Didier Drogba entered the fray at the expense of Mikel. A slight reshuffle in midfield saw Willian operate more in a central role.
A howler of a back pass by Ward-Prowse wasn't capitalised on by Chelsea, as the ball fell invitingly inside the penalty area to Costa, the Brazil-born Spain striker slipped and hit the deck, much to the relief of the home side's fans.
Koeman made his final substitution on 77 minutes, replacing Ben Davis for striker Shane Long, perhaps hoping a home side counter-attack might prove fruitful.
Two minutes from time and Schniderlin hacked down Fabregas and received his second yellow card followed by a red card.
Mourinho threw on his third striker Loic Remy with the minutes ticking down in an almost desperate all-out attacking policy. He replaced Costa who had run himself into the ground for the Blues cause.
Drogba almost got his foot to a beauty of a Fabregas byline cross as the four minutes of added time eked down.
Teams; Chelsea, Courtois, Ivanovic, Luis, Fabregas, Hazard, Mikel, Schurrle, Costa, Matic, Cahill, Terry
Subs, Cech, Zouma, Ramires, Dfogba, Remy, Willian, Azpilicueta
Southampton; Forster, Yoshida, Schneiderlin, Fonte, Davis, Mane, Tacic, Wanyama, Alderweireld, Pelle, Targett
Subs, Davis, Gardos, Long, Ward-Prowse, Isgrove, Reed, McCarthy
Referee, A Taylor
Ends