Wayne Rooney was a constant threat throughout the match up front
By Pranav Soneji
Wayne Rooney notched his 99th goal for Manchester United as the Premier League champions opened up their title defence with victory over Birmingham.
The striker tapped in after his header from Nani's cross rebounded off the post back into his path on 34 minutes.
Ben Foster made a brilliant stop to deny Christian Benitez a goal on his Birmingham debut in the 77th minute.
Substitute Michael Owen missed a chance to open his account for United when he shot at Joe Hart in stoppage time.
Although not one of their most convincing performances, United created enough chances to emphasise the depth of their attacking options, despite the loss of Cristiano Ronaldo to Real Madrid.
Rooney relishing central role
Rooney, in particular, was menacing with the ball at his feet, making intelligent runs when his team-mates were in possession.
Deprived of first-choice centre-backs Nemanja Vidic and Rio Ferdinand, who will have a scan on Monday on a calf injury sustained in training, United boss Sir Alex Ferguson moved John O'Shea into central defence alongside Jonny Evans, with Fabio da Silva promoted to right-back.
Paul Scholes returned to the centre of midfield, while new signing Antonio Valencia slotted into the sizeable hole vacated by Ronaldo on the right.
The daunting prospect of opening up against the Premier League champions convinced Birmingham manager Alex McLeish to start with a five-man midfield, with Cameron Jerome as a solitary striker.
Their defensive tactics offered United ample opportunities to exploit space in midfield, with Darren Fletcher threading a precise ball for Nani to attack on the left after seven minutes, but the winger's right-footed strike was well saved by Joe Hart.
Rooney once again pressed Hart into action, this time with a dipping 20-yard strike on 12 minutes, acrobatically tipped over the bar by the on-loan goalkeeper.
Attempting to frustrate United's invention in midfield, Birmingham's defensive intentions unravelled when Rooney put the champions in the lead with a precise move starting on the half-way line.
The striker fed partner Dimitar Berbatov, who released Nani down the left and the winger's teasing cross was tapped in by Rooney after his initial hanging header rebounded off the right-hand post back into his path, with Hart well beaten.
But rather than break Birmingham's resolve, the goal invigorated their attacking intentions as Jerome fired a dangerous 20-yard deflected strike just past Foster's right-hand post.
The resulting corner saw Patrice Evra clear Franck Quedrue's glancing goal-bound header off the line, to the relief of the near-capacity Old Trafford crowd.
Phelan backs youngsters to replace stars
However, the visitors should have taken a two-goal cushion into the break, but Fletcher contrived to side-foot his 10-yard strike wide of the post after an excellent cut-back from Evra on the left.
Resisting the urge to replace Antonio Valencia after a largely anonymous first half, Ferguson instead introduced Ryan Giggs for Nani on the left at the start of the second half.
The change in personnel had little effect on Rooney, whose 30-yard half-volley was destined for the top left corner but for a two-handed parry from Hart.
Birmingham's tactics began to have their desired effect, with Barry Ferguson in particular dictating terms in midfield.
A powerful burst from Keith Fahey preceded a right-foot strike from 20 yards past the right-hand post, while McFadden exploited space on the edge of the box to shoot straight at Foster.
However, the visitors had Lee Carsley to thank when the midfielder cleared Berbatov's header off the line on 70 minutes.
McLeish upbeat despite defeat
The Bulgarian striker could have had a penalty minutes later when Stephen Carr appeared to tread on the striker's boot.
It proved to be Berbatov's final contribution, replaced by Owen with 15 minutes left, while McLeish introduced record £8m signing Benitez for Jerome.
The Ecuadorian striker made an immediate impact when he timed his run to perfection to beat United's offside trap 13 minutes from time, only to be denied by a wonderful one-handed diving save from Foster.
Rooney came close to his 100th goal in the 83rd minute, but Owen should have put the result beyond doubt when he was released through the middle by Rooney's chested flick.
But one-on-one with Hart, the striker's effort deflected off the goalkeeper's leg for a corner.
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