Jobi McAnuff scored deep into injury time to rescue a point for Watford.
The Hornets have not won at home since October 20 and were destined for another Vicarage Road defeat to Cardiff until the winger curled his strike into the top corner from the edge of the box in the third minute of added time.
Roger Johnson gave the visitors the lead in the first half but it was cancelled out just after the break by captain Jay DeMerit's close-range strike. Peter Whittingham restored the Bluebirds' lead minutes later with a fine solo run and shot but Watford fought back to grab a fortuitous point.
The home side, who started with Nathan Ellington and McAnuff after the pair impressed as substitutes during last weekend's win at Sheffield United, began brightly and had a couple of half chances in the opening minutes.
Tommy Smith hooked a ball into the area for Marlon King in the second minute but the striker's header was deflected just wide, and Ellington's teasing cross narrowly evaded Damien Francis two minutes later.
Cardiff made an equally lively start and did not appear to be missing the services of Robbie Fowler who failed a late fitness test on an ankle injury. In the opening minutes they created a slick sequence of passing on the right before Stephen McPhail volleyed just wide of the right hand post from the edge of the box.
In the 14th minute, Paul Parry broke free on the right but he attempted to shoot past the onrushing Richard Lee when a cross would have found Steven MacLean unmarked in the box, and his effort was well blocked by the goalkeeper.
That chance set the tone for the rest of the half and the galvanised visitors dominated.
The hosts had numerous chances to break forward in space but time and again their pass found a blue shirt instead of a yellow one.
Joe Ledley's header just over the bar on the half-hour mark should have been a warning to Watford but it was ignored at their peril and four minutes later Cardiff took a deserved lead when Johnson powerfully headed in Gavin Rae's cross from the right.
Watford dramatically improved in the second half and were level minutes after the interval when DeMerit latched on to Ellington's knock-down and rifled home from close range.
But it was not long before the Bluebirds capitalised on some sloppy defending and restored their lead. Damien Francis was dispossessed in a dangerous area in the 56th minute and Whittingham ran into the heart of Watford's defence before unleashing a powerful low shot into the right hand corner.
McAnuff forced Kasper Schmeichel into his first save of the game after an hour when he shot from the left of the box and Henderson headed Smith's cross inches over the crossbar.
In a tumultuous final five minutes which saw a Watford onslaught, Francis' header was directed straight at a grateful Schmeichel, who then tipped McAnuff's stinging shot over. McAnuff had another shot just wide before he struck a first time shot high into the far corner to cue wild celebrations.
Teams:
Watford Lee, Doyley, DeMerit, Jackson (Shittu 85), Stewart, Smith, O'Toole (Williamson 35), Francis, McAnuff, King (Darius Henderson 63), Ellington.
Subs Not Used: Poom, Ainsworth.
Booked: Stewart.
Goals: DeMerit 49, McAnuff 90.
Cardiff Schmeichel, McNaughton, Loovens, Johnson, Capaldi, McPhail, MacLean (Purse 86), Ledley, Whittingham, Rae, Parry.
Subs Not Used: Oakes, Blake, Ramsey, Hasselbaink.
Booked: McPhail.
Goals: Johnson 34, Whittingham 56.
Att: 17,014
Ref: Grant Hegley (Hertfordshire).