The FA Cup lived up to its billing as great drama when John Terry emerged as Chelsea's unlikely hero as East End slapstick exceeded West End farce in an error-strewn fourth round replay.

In a game plagued by mistakes, both defences seemingly attempted to outdo each other in their largesse as they traded self-imposed wounds to stand at 2-2 at Upton Park.

After Jermain Defoe's half-volley received a huge deflection off Terry, Hammers keeper David James was caught napping by a quickly-taken Jimmy Floyd Hasselbaink free-kick.

However, while his mistake was outdone by Chelsea keeper Carlo Cudicini's error in handing an open goal to Defoe, midfielder Don Hutchison returned the favour to substitute Mikael Forssell.

The match looked bound for extra-time before Terry put aside his recent tribulations, involving a charge of assault - which he denies - and a suspension from international selection, to force home a late winner.

It was the perfect antidote to his early deflection and having forced a fifth round tie at home to Preston, Chelsea could look back on their second unlikely comeback in the space of just four days.

Having initially recovered against Leicester last weekend to similarly triumph 3-2, they repeated the feat while playing just as badly.

Then again, Claudio Ranieri will argue that he is due a turn of good fortune.

That luck began when the team-sheets were handed in and Frederic Kanoute joined the suspended Paolo di Canio on the sidelines due to injury.

That meant Paul Kitson was paired alongside Jermain Defoe, while Chelsea fielded the most potent strike duo in the Carling Premiership, in Hasselbaink and Eidur Gudjohnsen.

None of them received a look-in in a dreary opening half-hour, however, before the Hammers' opening goal came out of the blue.

Terry failed to clear Steve Lomas's cross properly and when the ball dropped to Defoe, his half-volley looked to be heading off-target until it struck Terry and flew in off the underside of the bar, leaving Cudicini stranded.

That at least sparked an otherwise dreary game into life and Chelsea were soon level after Tomas Repka had been penalised for handball.

James was still lining up his defensive wall when referee Graham Poll stepped aside from in front of the ball.

Hasselbaink, who similarly struck with a fierce free-kick against Spurs in the Worthington Cup semi-final, did not hesitate as he blasted the ball into the opposite corner while James struggled to make up lost ground.

The Dutchman also came close soon afterwads with a long-range drive, while West Ham only just survived after the restart when James flapped at a corner to spark a goalmouth scramble.

However, Cudicini had no such luck when he spilled Hutchison's low cross straight into the path of Defoe, who needed no help this time to force the ball home from close range.

The visitors responded by bringing on strikers Gianfranco Zola and Mikael Forssell, who had similarly cme on at Filbert Street when their side were behind.

Within a couple of minutes, the move had again worked - but only after Hutchison virtually handed Chelsea their equaliser on a plate.

Albert Ferrer's deep cross was heading nowhere until Hutchison attempted to head the ball back to keeper James and thereby allowed Forssell to nip in and clip his shot past the exposed West Ham keeper.

James recovered to smother Hasselbaink's follow-up effort after spilling Forssell's initial drive, while Cudicini also partially redeemed himself in tipping over Hutchison's header.

Both sides came close to a winner, with Defoe and Zola just off target, while Christian Dailly struck the inside of the post and James produced a fantastic reaction save to deny Mario Stanic.

However, the best drama demands a twist in the tail and that was duly provided when Terry rose to head home a corner to seal Chelsea's unlikely success.

Teams

West Ham: James, Schemmel, Repka, Dailly, Winterburn, Sinclair, Hutchison (Labant 76), Lomas, Cole, Defoe, Kitson (Todorov 82).

Subs Not Used: Hislop, Moncur, Foxe.

Booked: Repka.

Goals: Defoe 38, 50.

Chelsea: Cudicini, Le Saux, Desailly, Terry, Ferrer, Stanic, Petit, Dalla Bona (Zola 61), Lampard, Hasselbaink, Gudjohnsen (Forssell 61).

Subs Not Used: de Goey, Jokanovic, Huth.

Booked: Stanic.

Goals: Hasselbaink 43, Forssell 65, Terry 90.

Att: 27,272

Ref: G Poll (Tring).