The Serbian striker entered the fray in the 77th minute and, despite standing out wide on the left, arrowed a speculative curling right-foot drive towards the penalty area.
There were no fellow forwards to attack the ball and there were no defenders to clear as it fell into the gleeful arms of goalkeeper Gabor Kiraly.
But, incredibly, the Hungarian let the ball go through his legs and, as he was on his goal-line, the ball trundled into the back of the goal. It was a comic moment in an otherwise dour London derby.
But for Chelsea, the number of goals is irrelevant, it's another three points.
Crystal Palace are in a relegation dog-fight and they had a game-plan to stifle Chelsea's midfield and hope for a counter-attack.
It worked for the most part but when Chelsea are gifted a goal like their third, it was always going to be an uphill battle.
But had top striker Andy Johnson been on better form, the Eagles could have gone into the break 2-1 up. As it was it was 1-1.
Chelsea took the lead in the 21st minute and it was a fantastic, trademark goal from England midfielder Frank Lampard.
The Blues were forced to play Paulo Ferreira at left-back as William Gallas was ill and did not start. The Portuguese international raced down the line fully 50 yards before scooping the ball further on to Joe Cole.
Cole cut inside and slotted the ball to Lampard. He collected the ball, moved five yards forward before unleashing a blistering right-footer which beat Kiraly and landed in the top right-hand corner of the net.
Until that point Lampard had had a subdued game by his standards.
He was culpable for the Crystal Palace equaliser three minutes before half-time. A Wayne Routledge corner fell short but Lampard completely missed his clearance in front of the near post.
The ball continued into the six-yard box and Eagles midfielder Aki Riihilahti reacted quickest to the loose ball and tucked his shot home from four yards out.
Johnson, the lone Palace striker, could and should have tucked away a stoppage-time effort.
Tom Soares floated over a deep ball into the Chelsea area. Johnson should have shown more composure when he trapped the ball but, with only Petr Cech to beat, the England striker screwed his shot wide of the far post.
It was the last chance for the Eagles to get anything from the match as Chelsea were back in front nine minutes into the second half.
Eidur Gudjohnsen kept hold of the ball in midfield before sliding an inch-perfect pass into the path of Cole. The former West Ham man, full of confidence of late, took a touch on the ball, and drilled a low, right-footed daisy-cutter across the path of Kiraly and into the back of the net.
Chelsea boss Jose Mourinho brought on Arjen Robben, Kezman and Tiago to see the match out.
The comical third goal was followed by Kezman's second deep into added-on time.
It was a typical gutsy striker's effort, slotting the ball home from a prone position in the six-yard box after the ball had ping-ponged inside the area.
MAN OF THE MATCH: Joe Cole (Chelsea) - Forever tracking back and doing his defensive work, the midfielder then popped up to put the Blues back on track with a fine goal. His overall contribution to the team cause was evident and he is a changed player from earlier in the season.