Salomon Kalou, right, is congratulated after putting Chelsea in front
Chelsea displayed all the resilience Luiz Felipe Scolari asked for as they came from a goal down to beat Southend in a tough FA Cup third round replay.
Adam Barrett headed the hosts into a shock lead from a corner, while Alex Revell also stung Petr Cech's palms.
But otherwise it was one-way traffic and after Michael Ballack's drive made it 1-1, Salomon Kalou slid in a second.
Nicolas Anelka and Frank Lampard each then poked in as Chelsea ran away with it, with Ipswich up next for the Blues.
Even Lampard's late strike was little more than Chelsea deserved, despite a brave backs-to-the-wall performance from Southend, who belied their position 56 places behind the Blues down in League One with a performance full of heart and determination.
In fact, had Chelsea not matched the endeavour of their opponents it might have been a different story, but as it was it was exactly the wrong time for Southend to face Scolari's men.
Sunday's Premier League defeat to Manchester United prompted declarations that Chelsea's title bid is over, while Scolari himself called this Cup tie as "the game of the year" - and right from the off it was clear the Blues were under no illusions as to the tie's importance.
It had initially looked as if Chelsea would have to wait for their chance to put Sunday's defeat to Manchester United behind them as referee Chris Foy called the game off due to fog just over an hour before kick-off - but the fog lifted and the game began on time after a change of decision by the referee.
And straight away the visitors went on the offensive, even with Didier Drogba and Deco dropped from the matchday 18, with Kalou and Ballack going close in the early exchanges and Joe Cole forcing a smart near-post save from Mildenhall after good work from Lampard.
So it was against the run of play when Southend took a shock lead - with Scolari's new zonal marking system exposed at the first opporunity - as Barrett headed in Stanislas's corner unmarked from eight yards.
That was not Southend's only chance of the half and it took a superb point-blank save from Petr Cech to keep out Alex Revell's header on 40 minutes to keep the scores level.
However, in truth, other than that it was near total domination of the football from Chelsea - and the only surprise was that their leveller was so long in coming.
Lampard had a great chance when his close-range volley was aimed straight at the keeper, while Joe Cole saw his effort on the rebound blocked and Anelka aimed a subsequent header narrowly wide.
As it was, the equaliser came giftwrapped by the Shrimpers, Mildenhall and Peter Clarke getting in each other's way and allowing the ball to fall to Ballack, who crashed home.
It was the German's first goal since his strike dumped Scolari's Portugal out of the 2008 World Cup at the quarter-final stage in June - evidence if it was needed of just how out of sorts he has been this season - but it was just the fillip Chelsea were after before half-time.
To their credit, the hosts refused to buckle in the face of their exalted opponents, but the second half followed a similar pattern to the first and it was not too long before the Blues were ahead.
Joe Cole was the orchestrator - the winger finding Kalou with an exquisite cross-field pass with the outside of his boot - and the Ivorian danced past two defenders before sliding into the far corner.
Scolari, whose exasperation was clear for all to see until that point, was visibly relieved - and the players also seemed to calm as they stroked the ball around with increasing confidence thereafter.
Anelka made it three late on with a neat finish after good work from Lampard and Kalou, and there was still time for Lampard to add a fourth with a close-range finish from Kalou's pass.
And so while Southend had caused the odd moment of alarm - Jean-Francois Christophe headed unmarked over early in the half - few could argue the Blues did not deserve the win, although a late knee injury to Joe Cole took the gloss off a win that otherwise earned the Blues some semblance of redemption after Sunday's loss to Man Utd.
Southend manager Steve Tilson:
"I could not be prouder of the players. It was fantastic to take the lead and we gave it a real go on the night.
"We knew that set-pieces were going to be our best chance to score and that proved the case - to be honest, I think the save from Revell was the turning point because if that had gone in, who knows what would have happened.
"At the end of the day, we have had a great run in the FA Cup with plenty of memories and the fans were superb."
Chelsea assistant first-team coach Ray Wilkins:
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"We're delighted - we are a very happy club. Contrary to what people think the spirit in the camp is absolutely superb.
"As you saw tonight, when the goals were raining in at the end, the players were all round each other, congratulating each other. And in the dressing room it is extremely buoyant.
"As for Didier Drogba, I haven't got a clue whether he will play at the weekend or not, but he is very much part of Chelsea football club and, if needed, he will pull the shirt on and play to a very high standard."
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