Birmingham City 1 Manchester United 3
Birmingham City's Carling Cup dreams were extinguished as a second-half collapse saw them slip to their second comprehensive defeat in three days.
Three top quality strikes by Louis Saha (two) and Ji Sung Park left the visitors in cruise control until Jiri Jarosik's late goal provided a glimmer of hope for Steve Bruce's side.
Bruce's dejected team have conceded seven goals in the last two games and will face their daunting Christmas fixtures with a large degree of trepidation.
However, while Birmingham were well beaten, they emerged with some of their pride intact as their spirit and resilience was far greater than the shambolic showing at Manchester City last Saturday.
But the same problems persist for Bruce's sieve-like defence and an attack that looks punchless, Jarosik apart.
It is hard to see what card Bruce is going to play until the opening of the transfer window and he will be praying that Birmingham's board inject substantial funds into his coffers, otherwise the odds are stacked against them winning a grim relegation battle.
David Sullivan had warned Bruce's squad that there would be departures when the transfer window opens next month in order to allow the manager the opportunity to revamp the team.
There were players who were playing for their futures and Bruce wielded the axe with Maik Taylor, Martin Taylor, Emile Heskey, Jarosik and Jermaine Pennant recalled to the starting line-up.
Birmingham looked under-standably nervous after Saturday's debacle at Manchester City and should have trailed inside three minutes. Once again, it was a set-piece that proved to be their undoing as Gary Neville's free-kick reached John O'Shea and his header reached Guiseppe Rossi inside the six-yard area.
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Rossi reacted quickly but his first-time shot rebounded off the bar with Maik Taylor well beaten.
Cristiano Ronaldo and David Dunn traded shots but it was the visitors who were looking more threatening and Saha spurned an easy opportunity to score when he headed Darren Fletcher's cross wide from five yards.
St Andrew's breathed a huge sigh of relief and the first tangible signs of self-belief were creeping into Blues' general play with the three-pronged goal threat of Heskey, Dunn and Jarosik starting to cause United concern.
Heskey came within a whisker of giving Birmingham a priceless lead when he was denied from point-blank range by Tim Howard. Dunn's tricky footwork drew a tackle from Neville and the ball rebounded to Heskey six yards from goal.
The big striker turned past Mikael Silvestre and unleashed a fierce drive but was denied by Howard's fingertips.
There was a genuine belief that Birmingham could engineer a result, as their confidence was growing appreciably. However, within 36 seconds of the restart, the visitors led through Saha.
The sight of Wayne Rooney entering the arena as a half-time substitute for Rossi was not what Bruce wanted to see but his heart sunk even further when Saha slid home a cross from Ronaldo at the far post.
Birmingham's frailty was there for all to see as, within five minutes, Park had scored his first goal for United.
The South Korean international latched on to a clever Saha flick and cut in from the right-hand side of the penalty area before unleashing a stunning left-foot drive past Maik Taylor into the top corner of the net.
Birmingham's confidence was shot to pieces and a series of misplaced passes led to growing disenchantment among home supporters.
Saha scored the goal of the evening to further sap Birmingham's fragile confidence.
Neville cut in from the right wing and played a neat pass into Saha's feet and he sidestepped Martin Taylor before unleashing a drive that left Maik Taylor grasping at thin air once again.
United's massed away following taunted Birmingham with chants of "we'll be back to send you down," referring to next week's Premiership clash.
Birmingham garnered a consolation goal with 15 minutes remaining when Jarosik rose highest to glance home Pennant's free-kick past Howard. ..SUPL: