Jak Alnwick's second-half howler allowed Watford to claim a 1-1 draw at Cardiff in the Sky Bet Championship.
The Cardiff goalkeeper's clumsy control of a harmless pass from centre-half Mark McGuinness gifted a 54th-minute equaliser to Hornets striker Vakoun Bayo.
The Bluebirds had taken the lead in the 26th minute through McGuinness, but never played with the energy they needed to bounce back from their midweek defeat at Middlesbrough.
Watford boss Valerien Ismael may feel his side deserved all three points but at least they stopped a run of three successive defeats.
Cardiff went into the game with injuries depriving them of significant firepower but that did not stop the hosts creating all the early chances.
Ike Ugbo, holding the forward line in the absence of others, came within inches of connecting with a rebound after Watford goalkeeper Daniel Bachmann palmed away a shot by midfielder Karlan Grant in the 17th minute.
Grant then found himself clean through at the midway point of the first half, only to blaze a careless attempt high over the crossbar.
The Hornets failed to heed the warnings, and in the 26th minute they fell behind to a goal that will have incensed manager Ismael.
A corner by Cardiff captain Joe Ralls was allowed to float to the far post where McGuinness converted a simple close-range volley.
Watford were not without threat up to the interval, but undid much of their good work in the final third with misdirected or overhit passes.
Striker Bayo dragged a clumsy shot wide when in space on the edge of the penalty area in the 33rd minute, but Watford saved their worst example of wastefulness until added time at the end of the half.
A back-pass by Cardiff defender Perry Ng was intercepted by Bayo, only for the Hornets man to lose control of the ball as he tried to round Alnwick.
There was a sense the equaliser might be coming, but nobody could have foreseen just how it would come in the 54th minute.
When a Watford attack broke down McGuinness played what looked a safe square ball to Alnwick, but the goalkeeper's touch was hideous, the ball bouncing off him to Bayo who this time punished the error by side-footing home.
The leveller was reward for a marked Watford improvement which saw Ismael's men take the ascendancy in midfield and offer far more menace going forward.
In the 78th minute another Cardiff error - this time a careless pass from Ryan Wintle - served up a glorious chance for Hornets substitute Tom Ince, who skied his shot into the stands.
Neither side could fashion a winner, and there was sense of frustration all round at full-time.
Cardiff City: Alnwick; Ng, McGuinness, Goutas, Collins, Siopis, Ralls (Robinson 57’), Wintle, Tanner (Bowler 71’), Ugbo (Sawyers 87’), Grant. Subs Not Used: Runarssson, Panzo, Romeo, Adams, R. Colwill, Evans.