Eden Hazand scored a lpenalty deep into added time to snatch a point from WBA who, up to that point seemed to have won the match and thus ended Jose Mourinho's unbeaten home record as Chelsea manager - his 100th game in face at Stamford bridge.
Despite taking the lead on the stroke of half-time from Samuel Eto'o, the home side looked lethargic and out of sorts.
WBA, marshalled by Steve Clarke who was Mourinho' former number two at the Bridge had his tactics spot on and it nearly resulted in a sensational victory.
The WBA defence was immense. Jonas Olsson and Claudio Yacob heading away each attack said their lives depended on it.
It was left to striker Shane Long and Stephane Sessegnon to show the Blues what they should have been doing by scoring the equaliser and then taking the lead with two second half goals.
Then, with three of the four minutes of added time gone, Ramires ploughed his was through the WBA defence, he came together with Steven Reid and went to the floor.
Referee Andre Mariner decided it was a foul, when many felt was a shoulder charge. But Chelsea still had work to do to convert the spot luck.
The coolest man in the stadium was undoubtedly spot kick taker Eden Hazard and he delivers the coup de grace, slotting home, sending Boaz Myhill the wrong way and preserving Mourinho' brilliant home record.
The opening exchanges can best be described as tentative from both sides.
Misplaced long balls, intercepted short balls, all consigned around the middle of the park.
No doubt WBA the happier of the two. Having that, on seven minutes, Morgan Amalfitano tried a shot from range - it was so weak it only just reached Petr Cech's byline.
Oscar reciprocated two minutes late, forcing Boaz Myhill into a save at least, although the effort was not goal-threatening.
WBA skipper Chris Brunt caught the long-range bug 12 minutes, but his effort sailed high and wide over Cech's crossbar.
Frank Lampard entered referee Andre Marriner's book for a silly late challenge on Shane Long on 15 minutes.
A beautiful crafted passage of play on 18 minutes involving the Blues's talented midfielders, Eden Hazard, Oscar and Willian almost saw striker Samuel Eto'o force Myhill into a save but the Cameroon's header, from eight yards out was a glancer rather than a directional one and it inched over his crossbar.
Claudio Yacob received a yellow on 29 minutes for bundling over Hazard. Oscar took the free-kick from 25 yards out and it appeared to be arrowing into the top left hand corner of Myhill's goal, but the goalie managed to get across his goal and tip the ball away for a corner.
Myhill was soon in action again, punching out a free-kick from Lampard and then clearing from Oscar as the Blues piled on the pressure.
Gareth McAuley was dispossessed of the ball in midfield by Eto'o with 10 minutes of the half remaining and the ball fed to Oscar. But the midfielder fluffed his lines and zipped his effort, from just outside the WBA penalty, area high and wide into the Shed End stand.
But just as the fourth official was putting up the three minutes extra time, Hazard fired a low drive from the edge of the WBA area, Myhill could only parry the ball and while Liam Ridgewell dithered on the ball, arch poacher Samuel Eto'o plundered and slid the ball into the net to put the Blues 1-0 up.
Eto'o as given a yellow card for his crowd-sharing celebration.
Oscar produced a brilliant defence-splitting ball from wide on the right on four minutes after the restart. Hazrad, beat the offside trap but just failed to take the ball under control, as it inched back to Myhill.
With the game entering into another sleep-inducing phrase, it was enlivened in a slept-second, on 56 minutes, when Shane Long got in front of Cahill and directed a Yacbo cross, from eight yards out towards goal.
The ball beat Cech but plonked it self off the foot of his right post and was cleared to safety.
Sensing that Chelsea had lost their grip on the game, WBA forced ever closer to the home side's goal and hit their reward on 60 minutes.
Cech produced a brilliant save from a powerful header from McAuley, only to see Long out jump John Terry at the goalkeeper's left hand post and head home the equaliser from six yards.
Jose Mourinho decided to being in striker Demba Ba within two minutes of losing the lead with ineffectual Lampard making way.
Chelsea reverted to a more conventional 4:4:2 with Oscar and Ramires the central midfield partnership and Hazard and Willian, out wide, supporting the front two of Eto'o and Ba.
As the Blues pushed forward on another raid, Chelsea were caught cold on the counterattack on 68 minutes.
Ivanovic had the ball taken off him in midfield and the ball was quickly pushed forwards. It ended up via a a Ridgewell pass to the left boot of Stephane Sessegnon. He produced a daisy-cutter, which had minimum power but it some how found its way under the prone body of Cech and into the back of the net to put the visitors 2-1 up.
The fault certainly started with Ivanovic, but even so, Chelsea had plenty of time to regroup and Cech will definitely feel he was at fault.
Juan Mata and Mikel were quickly rushed into the pitch with Azpilicueta and Oscar hauled off.
Chelsea forced the pace in search of an equaliser and on 78 minutes Myhill defied Cahill with a wonderful reflex save from close range.
Long was then sacrificed by Steve Clarke for the fresh legs of Victor Anichebe.
While Myhill was producing great saves, it did not help the Chelsea cause when Willian, with 10 minutes to go, decided to head over the goal, unchallenged from six yards out.
Amalfitano got a yellow for fouling Ramires as the visitors dropped back to their final third, clinging onto their precious lead.
No Chelsea player was in six-yard box when Cahill arrowed over a byline cross as the minutes ticked down with three to go.
WBA squanderd a great chance to finish off the Blues on 90 minutes but Brunt skied the ball over the goal after going on a 60 yard run.
Then sensationally, deep into added time a lung-busting run by Ramires was ended by Steven Reid, who bundled over the Brazilian.
Referee Marriner seemed to take ages before making his decision, but then pointed to the penalty spot, much to the dismay of the visiting fans who like the players felt that Reid has shoulder charged Ramires.
But up stepped Hazard, to send Myhill the wrong way to secure a point and Mourinho's unbeaten home league record.
Just how many wake-up calls this Chelsea side need is anybodies guess. But the point earned, might just prove vital come the end of the season.
Chelsea, Cech, Ivanovic, Ramires, Lampard, Oscar, Hazard, Willian, Cahill, Terry, Azpilicueta, Eto'o
Subs, Schwarzer, Cole,
His, Mata, Mikel, De Bruyne, Ba
WBA, Myhill Reid, Olsson, Yacob, Ridgewell, Long, Brunt, Amalfitano, Mulumbu, McAuley, Sessegnon
Subs, Daniels, Popov, Morrison, Anichebe, Vydra, Dawson, Berahino
Referee, Andre Marriner