Dimitar Berbatov grabbed his third hat-trick of the season as Manchester United hammered Birmingham 5-0 an embarrassingly one-sided Premier League contest at Old Trafford.

Also starting the move that led to Ryan Giggs’s goal, Berbatov was imperious in all aspects of his game, leading the line with strength and poise and finishing with his head and boot as he carved a poor Birmingham side apart.

Nani added a late fifth in a match that plunged Birmingham back into a relegation dogfight and sent out a title warning to United’s rivals.

It should have been more. Ben Foster was overworked in the Birmingham goal, Nani was wasteful with his shooting and crossing and - when he did get his final ball right - Wayne Rooney missed an absolute sitter as his strange season continues.

Birmingham, for their part, rarely threatened and only looked like scoring when Keith Fahey bettered Rooney’s miss when he kicked air at the far post with the goal at his mercy.

The result keeps United top with games in hand on their rivals. Birmingham hover one point above the drop zone, 16th but with a game in hand on sides below.

A rampant, strutting United dominated from the outset as Berbatov in particular played like football was going out of fashion.

They took the lead within 90 seconds, the first of countless Giggs corners flicked on by John O’Shea and nodded over the line by Berbatov as Birmingham marked zonally but forgot to attack the ball.

Three minutes later Berbatov was denied by the legs of Foster, the former United keeper atoning for a rotten clearance with a smart save from 12 yards.

Birmingham barely touched the ball, with David Bentley the only real threat from wide positions but not helped by a confused Matt Derbyshire, not physically up to leading the line as a lone striker.

United bombarded the Blues goal and thought they had a second when Chris Smalling - in for the injured Rio Ferdinand - headed a corner against the manhood of poor David Murphy, amd Nemanja Vidic rolled the loose ball home, but referee Mike Jones blew for an infringement in the crowded penalty area.

Bentley rattled United briefly with some excellent crosses from the left flank but his team-mates’ movement did not match his delivery and, scare over, the hosts doubled their lead in style just after the half hour.

Rooney charged from halfway, finding Berbatov all too easily and the Bulgarian effortless cut inside Roger Johnson and drilled a low shot past Foster to double his and United’s haul.

It was game over but United were happy to continue their assault. Rooney sent Berbatov through with a cheeky stepover but the ex-Spurs man was unable to add to what is now his record Premier League season haul of 16 when he smacked the ball wide.

They did get a third before the break and it was worth delaying the customary half-time trip to the bar.

After being played a faint hospital ball by Bentley, Murphy’s poor touch allowed Berbatov to hook the ball with a slide-tackle, before exchanging a slick one-two with Rooney. The England striker picked out Giggs at the far post, whose rasping drive into the roof of the net left Foster a spectator.

It was a delightful team goal - Rooney backheeled the ball during the move, while Berbatov’s determination to kick it all off typified his new-found all-action approach this season - and a vital one in that it extended United’s goal difference well beyond Arsenal’s, a statistic that may well be relevant at the end of a tight season.

Birmingham started the second half gamely enough but without asking any questions of Edwin van der Sar. United, meanwhile, should have had an early fourth but Rooney inexplicably headed wide from point-blank range when Nani’s cross put the goal at his mercy.

Bentley went close for Birmingham, drilling just wide after squeezing past Anderson and Fabio da Silva, but United added a fourth when Berbatov rifled in a finish off the bar after superb work by Rooney and Giggs on the left.

Then came Fahey’s miss, as the Irishman somehow failed to convert at the far post after Van der Sar saved Derbyshire’s low drive, sparing Vidic’s blushes as it was his blunder that let the former Blackburn forward in.

In the closing stages Nani, Michael Owen, Berbatov and Rooney all had half-chances, with Nani compensating for his earlier profligacy when he hammered a wicked low drive into the bottom left for a fifth: he spurned several more chances afterwards, but it mattered little with the match well won.

United stay unbeaten in the Premier League after the win, with Birmingham falling to their seventh loss of the campaign.