A typical piece of opportunism from Ruud van Nistelrooy earned Manchester United their sixth successive Premiership win - and moved them to within three points of leaders Arsenal.

Van the Man struck his 26th goal of the campaign early in the second half after some slack defending to kill off a spirited challenge from Steve Bruce's side at St Andrews.

Birmingham matched their more illustrious opponents in the opening 45 minutes with their aggressive and committed approach which had been demanded by manager Steve Bruce.

Stephen Clemence clearly showed he is benefiting from a greater level of first-team match fitness after being frozen out at Tottenham.

United looked to be frustrated at struggling to create any openings despite the impressive promptings from the centre of the park of Juan Sebastian Veron.

But it was a different story after the break with Ferguson's side grabbing the crucial early goal and then dominating the possession as Blues found it difficult to sustain the first-half tempo.

While United are still very much in the race for the title, Blues are now very much embroiled in a relegation battle.

For all their passion and determination, the harsh statistics are that they have now collected just one point from the last six matches - with home encounters with Chelsea and Liverpool next on the agenda.

United were the first to settle and Blues 'keeper Nico Vaesen, recalled in place of Ian Bennett, had to come smartly out of his area to deny Paul Scholes after he had dispossessed Jeff Kenna.

Gary Neville had an effort blocked by Jamie Clapham and Ryan Giggs failed to make full contact on his first time effort from 20 yards out which was easily dealt with by Vaesen.

Morrison conceded a free-kick in a dangerous position some 22 yards out after a foul on Roy Keane but Beckham's resulting effort cannoned off the defensive wall at the expense of a corner.

The England skipper tried his luck again from 25 yards after Christophe Dugarry had brought down Giggs but he was again off target as his shot curled over the crossbar.

But, although United were shading the possession, they did not have matters all their own way as Blues tackled and fought as if their lives depended upon it.

City had their sniff of a chance after 28 minutes with Stern John sending a header wide at the near post from a Kenna right-wing cross.

Then it needed a goalline clearance from Mikael Silvestre to keep United on level terms after 31 minutes.

Clemence sent over a right-wing corner which was met by a firm header from 10 yards out by Dugarry only for Silvestre to deny him his first goal for the club.

Blues were now enjoying their best spell of the game and a teasing cross from Robbie Savage only just eluded Morrison.

But a dummy from Giggs left Silvestre with a shooting opportunity at the other end only for his rising effort to go wide of Vaesen's post.

Then Scholes went close to giving United the lead when he took a cross from Beckham into his stride and thundered a shot against the crossbar with Kenny Cunningham able to clear the rebound.

Clemence became the first player to be yellow-carded after 48 minutes for a clumsy challenge on Veron.

Then after 56 minutes that man van Nistelrooy showed his predator's instinct to give United the lead.

A right-wing cross from Scholes found its way to Silvestre at the far post and he had time to bring the ball down before finding van Nistelrooy in the centre.

The Dutchman had two defenders around him but he was still able to swivel and drill a low shot past Vaesen into the corner of the net.

Scholes could have made it 2-0 after seizing onto a low cross from Giggs but he sent his shot from barely 10 yards over the crossbar.

United were now in the ascendancy although Keane was booked for the first time in 11 matches since returning from his long injury lay-off for preventing Dugarry from taking a quick free-kick.

Teams

Birmingham: Vaesen, Kenna (Devlin 84), Cunningham, Upson, Clapham, Damien Johnson, Savage, Clemence, John (Lazaridis 62), Dugarry, Morrison (Kirovski 78).

Subs Not Used: Bennett, Swierczewski.

Booked: Clemence.

Man Utd: Carroll, Gary Neville, Ferdinand, Brown, Silvestre, Beckham, Keane, Veron, Giggs, Scholes, van Nistelrooy (Solskjaer 82).

Subs Not Used: Phil Neville, Butt, Ricardo, Forlan.

Booked: Keane.

Goals: van Nistelrooy 56.

Att: 29,475

Ref: S Dunn (Avon).