West Ham striker Marlon Harewood's emphatic winner booked his side's place in the FA Cup final against Liverpool at the expense of Middlesbrough.
Harewood gathered Dean Ashton's 78th minute knock-down and held off defender Gareth Southgate before powering an angled drive into the roof of the net.
Franck Queudrue had a free-kick punched away as Boro tried to respond.
Chris Riggott had an excellent late chance but scuffed a shot wide as an edgy West Ham held on.
There was supposed to be a minute's silence before the game following the death of ex-West Ham boss John Lyall earlier in the week but some Hammers fans seemed to want to pay their respects by chanting his name.
When the match started, Boro burst out of the blocks and continually had the Upton Park outfit back-pedalling.
The Teessiders made light of having three days less than their rivals to prepare for the game as Jimmy Floyd Hasselbaink had a blocked header sandwiched in between two Fabio Rochemback shots.
There was plenty of promise to Boro's build-up play but they were let down by the poor touch of their strikers Hasselbaink and Yakubu as moves broke down in the final third.
West Ham seemed to have gradually worked their way into the match only for their rivals to quickly regain control.
And manager Steve McClaren's Boro will have been disappointed not to take the lead when Queudrue met an inswinging Stewart Downing corner eight yards out but headed over.
The Riverside club suffered the blow of keeper Mark Schwarzer being forced off because of injury but, despite a Yossi Benayoun strike going over, they dominated the first half.
West Ham improved after the break and put Boro under pressure, with Ashton going close when he headed a corner on to the top of the crossbar from six yards out.
McClaren's side had chances on the counter-attack but the delivery from playmaker Rochemback let them down.
Hammers skipper Nigel Reo-Coker flashed an angled 25-yard strike agonisingly wide as the intensity of the match increased - with the London side looking the more likely to score.
And they duly did so when Harewood thundered in his shot after Ashton headed down Anton Ferdinand's long ball.
West Ham boss Alan Pardew scored a winner against Liverpool at Villa Park to send Crystal Palace into the FA Cup final in 1990 and his side held on to secure a place in Cardiff for this season's 13 May showdown.
The victory also assured the Hammers of a place in next season's Uefa Cup.
Middlesbrough: Schwarzer (Jones 42), Riggott, Southgate, Queudrue, Parnaby, Rochemback (Parlour 75), Boateng, Downing, Taylor (Maccarone 80), Hasselbaink, Yakubu.
Subs Not Used: Ehiogu, Bates.
Booked: Rochemback, Maccarone.
West Ham: Hislop, Ferdinand, Gabbidon, Collins, Konchesky, Benayoun, Mullins, Reo-Coker, Etherington (Newton 89), Harewood, Ashton (Zamora 85).
Subs Not Used: Walker, Scaloni, Sheringham.
Booked: Reo-Coker, Ashton, Harewood, Collins.
Goals: Harewood 78.
Att: 39,148
Ref: M Riley (W Yorkshire).