Striker Dean Ashton, signed from Norwich for £7million during the January transfer window, was the Hammers hero in their last eight-victory at Manchester City.
Ashton repaid a massive slice of his club record transfer fee, scoring his fourth and fifth goals for the club which were the most important strikes since his big money move.
While the Hammers were celebrating their famous victory it was a night when City's 30 years of hurt resurfaced. That is the length of time since they last won the League Cup, their last success in a major knockout competition.
And it is 25 years since City last made it to the semi-finals of the FA Cup, the year they lost in the final to Tottenham following that never to be forgotten replay at Wembley.
City desperately lacked fire-power with Andrew Cole, new £6million signing Georgios Samaras and Antoine Sibierski all ruled out through injury with Darius Vassell and Bradley Wright-Phillips offering little threat up front.
With Trevor Sinclair and Claudio Reyna also ruled out, City manager Stuart Pearce's side was badly depleted. The Hammers, by contrast, only had central defender Anton Ferdinand missing after he was hurt in Saturday's home defeat by Portsmouth.
City made a bright start with Kiki Musampa forcing Hammers keeper Shaka Hislop to make a smart save in the second minute.
But the early sparkle soon disappeared and City's cause was not helped when Stephen Jordan limped off midway through the opening half.
The Hammers made the vital breakthrough in the 41st minute when Ashton started and finished the move as he fired home a shot from the left side of the penalty area which disappointingly for City found a way past keeper David James at his near post.
And when Paul Konchesky headed off the line to deny Sun Jihai shortly after the Hammers took the lead it was clearly not City's night.
And their cause all but disappeared 11 minutes after the restart when Sun Jihai was sent off for striking out at Matthew Etherington.
The Hammers started to take control with Etherington's drive striking the top of the crossbar and it was no surprise when Ashton secured victory in the 69th minute rounding off a neat move involving Nigel Reo-Coker and Yossi Benayoun.
In a last desperate bid to retrieve something from the game, Pearce took off Wright-Phillips and switched defender Richard Dunne to City's frontline in a bid to give them more strength and aerial threat.
City's injury troubles deepened even further in the closing stages when key midfielder Joey Barton limped off.
But with little over five minutes remaining Musampa handed City a lifeline with a terrific volley from the edge of the penalty area after substitute Lee Croft had cut back a cross from the right.
Sadly it was too little too late, though it gave the City fans renewed hope in the dying stages they might force a replay.