For the second time in nine months, Jose Mourinho sauntered into the Theatre of Dreams and created a nightmare for Manchester United.

Sir Alex Ferguson still shudders at the memory of Porto's shock Champions League victory at his side's expense last season.

Now Mourinho has moved much closer to home and proceeded to wreck Ferguson's impeccable domestic semi-final record on Wednesday night as Damien Duff's late winner booked Chelsea a Carling Cup final date with Liverpool and kept them on target for an unlikely quadruple.

It was unfortunate for United goalkeeper Tim Howard that an absorbing contest which looked destined for extra-time should eventually be settled by his mistake.

A string of excellent Howard saves were largely responsible for the hosts still being in the contest when Duff drifted a touchline free-kick deep into a packed Red Devils' penalty area.

Howard failed to come and with the defence in front of him remaining static, the ball simply bounced in off the far post.

For Ryan Giggs at least it was a bitter blow as the Welshman had ignited the hosts with a sublime first-time finish midway through the second half that levelled Frank Lampard's opener.

Giggs will rarely score a better goal than the one he lofted over Petr Cech after he had run on to Gary Neville's return ball.

But while United might claim to be hard done by, it was Chelsea who produced the most incisive play and if any side deserved to win such a hard-fought contest, it was them.

While Ferguson could plausibly claim defeat for the visitors would have no discernible effect on their seemingly unstoppable march to the title, the Scot knew anything other than victory for his own side would render their chances of overhauling Chelsea's 11-point lead virtually impossible.

At the same time, it would also end the Red Devils hopes of lifting one of the three pieces of silverware they still have a realistic chance of winning - which is why Roy Keane, Rio Ferdinand, Ryan Giggs and Gary Neville were given a rare League Cup appearance.

Of the players available, only Wayne Rooney was omitted from what constituted United's strongest side, although even the strength of that team selection was trumped by Mourinho, whose team was the best he could choose.

Lampard gave the hosts a warning of what was to come early on when he spurned a virtual mirror image of the goal which eventually gave Chelsea the lead.

Duff was the provider on that first occasion, slipping a pass back to the England midfielder - who failed to realise how much time he had and scuffed a poor shot wide.

As actual chances went, it was the last clear cut one either side had until Lampard found the net just before the half-hour mark.

In between though, both sides attacked with zest, kept at bay by the best two defences in the top flight.

Lampard's goal, from Didier Drogba's square pass, put a totally different complexion on the game, forcing United to try and break Chelsea down. If effort alone counted for anything, the hosts would have achieved their aim.

As it was, the best the best they could come up with was a loud, legitimate and unsuccessful penalty shout when Wayne Bridge felled Quinton Fortune.

A similar story began to unfold after half-time as United pushed forward and Chelsea looked more likely to score.

Had it not been for Howard's heroics, the Red Devils would have conceded a killer second long before Giggs' inspirational intervention.

The American keeper may now be a confirmed second choice behind Roy Carroll but his form recently has been excellent, which only made his late, crucial blunder all the more surprising.

Twice he kept United in the hunt, scrambling away a goalbound Lampard effort, before earning top marks for a feet-first stop which denied Robben.

In truth, the keeper shouldn't have been given much of a chance but Tiago opted for an ill-advised stepover when Drogba rolled across an inviting square pass, forcing Robben to shoot when he was far better placed.

Giggs' stunning effort ensured the error, such as it was, was severely punished - but if United thought their equaliser would unsettle their visitors, they were badly mistaken.

Chelsea responded by ignoring the frenzied atmosphere and clinically looking for a second. They got it too, although they benefited massively from Howard's major misjudgement.

Typically, United rallied and it needed a goalline clearance from Wayne Bridge to deny Mikael Silvestre and a brilliant Petr Cech save to deny Cristiano Ronaldo before Mourinho was able to celebrate yet another famous night at Old Trafford.

Teams:

Man Utd Howard, Gary Neville, Ferdinand, Silvestre, Heinze, Ronaldo, Keane, Scholes, Fortune (Rooney 59), Giggs, Saha.

Subs Not Used: Phil Neville, Brown, O'Shea, Ricardo.

Booked: Keane.

Goals: Giggs 67.

Chelsea Cech, Paulo Ferreira, Gallas, Terry, Bridge, Makelele, Lampard, Tiago, Robben (Cole 90), Drogba (Gudjohnsen 68), Duff (Jarosik 87).

Subs Not Used: Cudicini, Huth.

Booked: Makelele.

Goals: Lampard 29, Duff 85. Agg (1-2)

Att: 67,000

Ref: R Styles (Hampshire).