Lee Bradbury's first-half thunderbolt was enough to earn Southend their first Coca-Cola Championship away win and heap more misery on out-of-sorts Cardiff at Ninian Park.
Bradbury blasted home strike partner Freddy Eastwood's knockdown from 20 yards midway through the first period and rock-bottom Southend held on for the first success on their travels in 14 attempts following promotion.
Free-falling Cardiff, who hit the woodwork twice, have not won in the league since November 11, but had only lost once on home soil before Southend's visit.
Dave Jones' side have now gone 12 games without a win and looked a shadow of the side that started the season so strongly.
Jones made one change from the side that held Tottenham to a goalless draw in the FA Cup last week, with Kevin Campbell in for the suspended Steven Thompson.
Southend midfielder Luke Guttridge started in place of the suspended Alan McCormack as Shrimpers manager Steve Tilson also made one enforced change.
Cardiff made a forceful start with Darren Purse and on-loan Arsenal defender Kerrea Gilbert going close with headers inside the opening 10 minutes, the latter's well-held by Southend goalkeeper Darryl Flahavan.
Flahavan held on to Riccardo Scimeca's header from Joe Ledley's cross soon after, but for all their early possession Cardiff fell behind.
Eastwood's knockdown 20 yards out fell perfectly for Bradbury, who rifled the ball into the top corner for his second goal of the season.
Michael Chopra flashed a left-footed shot over the bar but Cardiff were dealt another blow when Campbell was forced off injured in the 26th minute and replaced by Andrea Ferretti.
Cardiff's Willo Flood fired over and saw another long-range effort blocked, but the visitors were not content to sit back on their lead.
Guttridge forced Neil Alexander to save with a header from 12 yards, Loovens then scooped the ball onto the crossbar from Flood's near-post corner and the latter brought a smart save from Flahavan with a shot from 20 yards.
Midweek signing Peter Whittingham made his Cardiff debut early in the second half for the injured Kevin McNaughton before Bradbury went close to adding a second for Southend.
Flahavan kept Southend's noses in front with a flying save to tip Scimeca's 30-yard piledriver round the post and then held Ferretti's long-range effort as Cardiff cranked up the pressure.
Whittingham fired over from 20 yards and then crossed for Ferretti, who saw his header hit the post.
Southend's attacking forays were now few and far between, but Eastwood rifled a long-range shot just over before Flahavan denied Ferretti again, the Italian firing in from the edge of the penalty area.
Jones threw on Luigi Glombard for Flood in the closing stages but it was Southend again who finished stronger, with substitute Matt Harold trying his luck from distance.
Whittingham blazed over for Cardiff in the second minute of time added on, but there was to be no breakthrough for them.
Cardiff Alexander, Gilbert, Purse, Loovens,McNaughton (Whittingham 52), Flood (Glombard 82), McPhail,Scimeca, Ledley, Chopra, Campbell (Ferretti 26).
Subs Not Used: Forde, Johnson.
Southend Flahavan, Hunt, Barrett, Clarke, Hammell, Gower,Maher, Guttridge, Campbell-Ryce (Hooper 68),Eastwood (Francis 85), Bradbury (Harrold 86).
Subs Not Used: Welch, Sodje.
Goals: Bradbury 23.
Att: 13,822
Ref: S Tanner (Somerset).