RECORD buy Ugo Ehiogu was the villain of the piece as Middlesbrough suffered another Cup calamity at Selhurst Park.
Ehiogu gave away the penalty which brought Wimbledon level in the 75th minute after Hamilton Ricard had given Boro an interval lead with a superb strike.
And £8m Ehiogu effectively condemned Boro to defeat when he was sent off in disgrace in the eighth minute of extra-time for landing a vicious right hook on Dons' defender Mark Williams - only two minutes after Jason Euell had put the First Division side in front.
Euell rammed home the rebound after defender Colin Cooper had blocked his initial effort.
Substitute Jonathan Hunt added a third in the 112th minute with a 25-yard drive which escaped the grasp of keeper Mark Schwarzer and went in via a post, to ensure that Terry Venables tasted his first defeat as Boro boss in what proved an unlucky 13th game in charge.
The Dons, who knocked Boro out of the Worthington Cup this season, now face a fifth-round trip to Second Division Wycombe on Saturday.
Ricard had produced another moment of FA Cup brilliance on the stroke of half-time to offer Boro hope.
The Colombian striker, whose stunning winner at Bradford in the third round was voted goal of the month on Match of the Day, reprised his party piece.
Skipper Paul Ince beat Trond Andersen to the ball to find Ricard, who cleverly dug it out from inside the 'D' to lift a high shot to the right of keeper Kelvin Davis.
Up to then, it was the one flash of genuine inspiration in a largely insipid game watched by a crowd of only 5,991 - 1,557 of whom were Boro fans.
Ehiogu, a goal-scoring hero on his return to Aston Villa last Saturday, found himself in the dog-house this time.
Referee Mike Dean wasted no time in pointing to the spot when Ehiogu pulled back the goal-bound Euell.
Substitute Neal Ardley convincingly converted the penalty with a rasping right-footed shot which ripped into the roof of the net.
It came just a minute after Venables had elected to withdraw Ricard in favour of rookie midfielder Mark Hudson.
With extra-time and the possibility of penalties looming, Boro's head coach was forced to rethink his tactics and send on leading scorer Alen Boksic in place of Brian Deane eight minutes from the end of normal time.
And Boksic was agonisingly close to clinching the tie in the last minute when he dragged his shot just wide of the far post.
Nine-goal Boksic, virtually discounted by Venables 24 hours before the game, managed to make the substitutes' bench despite a nagging groin problem.
Deane, who replaced the Croatian when he was taken off in the second half of the 1-1 draw against Villa, made his first start since the December 16 home win over Chelsea, when Venables' proud run began.
Central defenders Ehiogu and Gianluca Festa passed fitness tests, but midfielder Paul Okon and wing-back Keith O'Neill were ruled out.
Phil Stamp and Dean Gordon - back at his former Crystal Palace haunt - were drafted in, with Robbie Mustoe taking the place of eye-injury victim Christian Karembeu.
In front of a predictably sparse crowd and on a pitch which began to cut up quickly, Boro carved out the first real opening on the quarter hour when Ince sent a drive flashing across goal that Ricard got a touch to as it flew wide.
But there was precious little else to excite the meagre gathering on a night when the so-called magic of the Cup again failed to capture the imagination of the public.
If the goalless encounter between the sides a week earlier was a bore draw, the early exchanges second time around proved even more mind-numbing.
To add to the tedium, there was a delay while Wimbledon midfielder Damien Francis received treatment before being stretchered off following a crunching block on the edge of the Boro area.
The game briefly sparked into life shortly after the half-hour mark, but in keeping with the scrappy nature of proceedings it was a mistake which produced a chance for Boro.
Centre-back Mark Williams squandered possession to Deane and when his low cross eluded all, Curtis Fleming whipped the ball back in from the right for Stamp to connect with a firm header which went straight at keeper Kelvin Davis.
The Dons responded immediately with a low drive from Gareth Ainsworth that was comfortably dealt handled by Schwarzer.
Ricard, as he so often does, then conjured a bolt from the blue to hand Boro an improbable lead, before Ainsworth was booked for a foul on Colin Cooper.
Boro were forced to make a change of their own when Andy Campbell came on for the limping Stamp at half-time.
But it was the home side who showed first after the break, Jason Euell firing an angled shot wide before Ardley, the replacement for the unfortunate Francis, unleashed a 25-yard drive which Schwarzer was forced to get his body behind.
Mustoe joined Ainsworth in the book for a foul Dons' skipper Kenny Cunningham, and ten minutes later the home side were level.
Par Karlsson should have wrapped it up earlier for the Dons in the 84th minute, but fired wide from a great position
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