So much for the end of the dilettante era at Tottenham. The Carling Cup heroes arrived at St Andrews with their brains left behind at Wembley. A stiff breeze did not aid their morale and Birmingham needed no extra incentive to put a handsome victory between them and the upsetting events of a week ago, when Arsenal’s Eduardo suffered a broken leg.

A hat-trick by Mikael Forssell brought Birmingham their first win since Boxing Day and gave their fight against relegation a precious momentum. Spurs though, were abject, beyond the excuse of last week’s trophy or Thursday’s Uefa Cup last-16 match against PSV Eindhoven. Forssell scored early in each half as Tottenham’s defence dithered, while Seb Larsson’s delightful free kick was the pick of Birmingham’s goal feast. Jermaine Jenas’s late goal was no consolation for Juande Ramos or the vociferous Spurs fans.

The fall-out from the injury to huge lead. Eduardo a week ago could still be felt around St Andrews before the match began. Both the Birmingham manager, Alex McLeish, and the chairman, David Gold, in their programme notes wished the Arsenal striker a speedy recovery and reiterated their full support for central defender Martin Taylor, who started his three-match ban yesterday. Banners told the Birmingham defender, whose tackle felled Eduardo, to keep his head up and, needing no incentive to rile the old enemy, Tottenham fans joined in the chorus of support and the universal condemnation for Arsène Wenger.

Tottenham seemed to sense the subdued mood and decided to revive their impersonation of the a side that was merely dabbling at taking things seriously. With one eye on the Uefa Cup match to come, Ramos rested three of his first team - Jenas, Robbie Keane and Aaron Lennon - and paired Darren Bent with a decidedly languid Dimitar Berbatov. Much to the delight of James McFadden, who had a profitable afternoon, Teemu Tainio was switched to left-back in a defence without both the injured Ledley King and Jonathan Woodgate. Radhi Jaidi, the Tunisia international, replaced Taylor at the centre of the Birmingham defence.

It did not take long for City to exploit Tainio’s poor positioning as a corner reached McFadden on the right. The Scot’s volleyed cross fell beautifully for Forssell. A flick of the striker’s blond head was enough to bring the home side a precious lead with just seven minutes on the clock.

That should have settled Birmingham, but far from it. Berbatov was allowed to control the ball, steady himself and lash a fierce right-foot shot against Maik Taylor’s left post and Jamie O’Hara, the pick of Tottenham’s midfield, had three decent efforts blocked or saved. Of Birmingham, little was seen other than some neat touches from McFadden, industry from Damien Johnson and some desperately agricultural defending.

Ramos was clearly aggravated by his side’s lethargy and replaced Tainio and Steed Malbranque with Keane and Jenas. However, caught on the break almost immediately, Tottenham found themselves outnumbered at the back as Gary McSheffrey curled a beautiful cross straight into the path of Forssell, whose shot was tipped over the bar by Paul Robinson at full stretch. It was a decent save by the England goalkeeper, but he should have been left stranded.

It did not matter. Just 10 minutes into the second half, Birmingham increased their lead. A driving run by David Murphy was halted illegally by Didier Zokora and, from the free kick, Larsson curled a right-foot shot past Robinson from 25 yards. It was not quite on a par with the Swede’s stunning winner at White Hart Lane in McLeish’s first game in charge, but close enough.

Within three minutes, Birmingham strolled deeper into the clover with a bizarre third, created by some Tottenham defending reminiscent of the pre-Ramos days and finished neatly by Forssell after Zokora had wrong-footed Robinson with a desperate lunge at Larsson’s low cross. Ramos ripped up Plan B; Birmingham tried to recall how to defend such a huge lead.

Sure enough, they retreated too deep, allowing Tottenham to pressurise at will. Taylor tipped over Berbatov’s 20-yard drive, Younes Kaboul and Tom Huddlestone also blasted decent chances over the bar and, in between, McFadden displayed the sort of insouciant intelligence that drove David Moyes to distraction at Everton. The Scot is a rarity, a genuine number 10, but pouting matches passing in roughly equal measure.

Still, Birmingham did more than hold out, Forssell claiming his first hat-trick in club football with a left-footed shot that trickled into the far corner.

Match stats

Player ratings: Birmingham: Maik Taylor 6; Kelly 5, Jaidi 5, Ridgewell 6, Murphy 6; Larsson 7, Muamba 5, Johnson 7, McSheffrey 6 (Parnaby 69min); Forssell 8 (Jerome 83min), McFadden 7 (Zarate 83min).
Tottenham: Robinson 6, Tainio 3, (Jenas 45min, 6), Kaboul 5, Chimbonda 5, Hutton 4, O’Hara 7, Huddlestone 5, Zokora 4 (Gunter 72min), Malbranque 5 (Keane 545min), Bent 4, Berbatov 4
Star man: Mikael Forssell (Birmingham)
Yellow cards: Birmingham: Johnson 45
Referee: L Probert Attendance: 26,055