A 90th minute goal from Peter Clarke earned League One Southend a shock third-round replay against Chelsea.
Salomon Kalou opened the scoring on 31 minutes when he rose unchallenged to head in Frank Lampard’s corner.
Didier Drogba twice failed to find the net when put clean through, while Juliano Belletti saw his header cleared off the goal-line by Johnny Herd.
The Blues were made to rue their misses when defender Clarke popped up inside the area to head in a long throw-in.
Moments earlier, Clarke sent a warning to last season’s Champions League finalists when his header from Herd’s cross bounced off the top of the crossbar.
The Shrimpers will be delighted having converted one of their two clear-cut chances, a mood which will be in stark contrast to Luiz Felipe Scolari’s side who should have romped to victory.
Drogba was put through on goal as early as the 10th minute but dwelled too long on the ball allowing Anthony Grant to produce a superb tackle to deny the Ivorian.
And a few minutes later, the striker shot wide with just Steve Mildenhall in the visitors’ goal to beat.
The Southend keeper also saved brilliantly from Ashley Cole’s 12-yard shot during another first-half assault by the Blues.
Chelsea pushed hard for a second goal after the break, with Mildenhall called into action again to stop Drogba’s effort, before the keeper was was forced to punch clear off the head of Ricardo Carvalho.
He could do nothing to prevent Belletti’s header creeping into the net, but fortunately for the shot-stopper, his team-mates and the travelling fans, Herd was on hand to clear off the line.
That interception proved crucial to Southend, 13th in League One, when Clarke nodded in at the far post to set up a Roots Hall replay on Wednesday 14 January.
Chelsea: Cudicini, Ferreira, Carvalho, Ivanovic, Ashley Cole, Belletti, Lampard, Mikel, Joe Cole (Di Santo 84), Kalou (Sinclair 87), Drogba.
Subs Not Used: Hilario, Mineiro, Anelka, Mancienne, Sawyer.
Booked: Mikel, Carvalho.
Goals: Kalou 31.
Southend: Mildenhall, Sankofa, Clarke, Barrett, Herd, Grant, Christophe (Moussa 74), McCormack, Stanislas, Barnard (Freedman 75), Revell (Laurent 75).
Subs Not Used: Joyce, Francis, Betsy, O’Keefe.
Booked: McCormack, Grant.
Goals: Clarke 90.
Ref: Stuart Attwell (Warwickshire).