Indeed, such was the misery of this thumping defeat that come the end Steve Bruce and not the Birmingham defence was most in need of protection. The Birmingham manager, sheltered by a significant police presence for virtually the entire second half, suffered the ignominy of an irate fan running in his direction before the interval. The supporter was belatedly stopped in his tracks though Liverpool most certainly were not.
Benítez's side, rampant throughout, cut through Birmingham effortlessly. This was nothing short of shooting practice for his side who cantered to their 22nd FA Cup semi-final and their first for five years.
Having gorged on the feast served up by Newcastle's and Fulham's benign defences, Liverpool arrived in buoyant mood. Two victories and eight goals in the space of four days imbued confidence in weary limbs; this was Liverpool's 53rd match of the season and their second in 72 hours following the triumph at St James' Park on Sunday, though they cannot have imagined that Birmingham would be so sympathetic to their cause.
Home fans were still taking their seats when Sami Hyypia, afforded the freedom of the Birmingham penalty area, headed past a startled Maik Taylor after 54 seconds. Not for the first time this season Bruce placed his head in his hands, gripped by a sense of disbelief. More suffering would soon follow. With just over four minutes on the clock the lead was doubled. Again there was no protection for Taylor as Peter Crouch stooped to head in his 11th goal in his last 24 appearances.
The announcer's pre-match attempts to clear-up uncertainty about whether there would be a replay in the event of a draw after 90 minutes had been rendered risible before Liverpool had chance to break into a sweat. This was no laughing matter for Birmingham fans, though. Few would have arrived envisaging a place in the semi-finals for the first time in 31 years but at the very least they expected to see effort and commitment from their embattled side. Not even the absence of nine first-team players was an excuse for their torpor in the early stages.
It was tempting to wonder whether David Sullivan had a premonition when he wrote in the match programme, "It would appear we have a mountain to climb." The Birmingham co-owner must have shared the alarm of home supporters when Crouch twice came close to adding a third before the eighth minute. Frustrations threatened to boil over at that point as fans vented their anger, though their misery would be compounded later in the half when Crouch inevitably doubled his tally.
Shortly after that third goal a Birmingham supporter slipped past the stewards and made his way towards Bruce in a scene similar to that which Steve McClaren endured at Middlesbrough last month. The offender was duly escorted from the pitch though he had made his feelings known. For Bruce this was nothing short of humiliation by a rampant Liverpool side.
Indeed the biggest concern on the Liverpool bench was Mohamed Sissoko's goggles. The Mali international was sporting protective eye-wear after he suffered retina damage in Lisbon a month ago, though his apparent discomfort prompted them to be discarded midway through the first half. His inclusion from the start was unexpected, though he had justified his place within seconds, flicking on Gerrard's free-kick for Hyypia to nod in.
Sissoko was also involved in Liverpool's second goal, feeding Gerrard on the right. The captain swept a fine ball into the area that Crouch, darting ahead of Kenny Cunningham, headed powerfully towards goal. Taylor was well-placed to save but made a hash of his attempts to keep the ball out, gifting Liverpool a second goal. The third, from the right boot of Crouch after Luis García evaded several challenges, inflicted further embarrassment.
The rout continued after the interval as Fernando Morientes slotted home inside the six-yard box after Steve Finnan, García and Gerrard combined. With 20 minutes remaining John Arne Riise joined the party, blasting home an unstoppable fifth. Liverpool hardly needed any help at that stage though Birmingham obliged all the same; Olivier Tébily turning Harry Kewell's cross into his own net before Djibril Cissé made it seven.