The question of the succession has been mentioned for a decade and more at Old Trafford.

Yet while Sir Alex Ferguson remains, as defiant as ever, at the helm, the manager has found new generations of players to epitomise and galvanise Manchester United. Once it was Roy Keane and David Beckham, later Ruud van Nistelrooy and then Cristiano Ronaldo. Now, beyond doubt, it is Wayne Rooney.

There are times when one man's exit prompts a frantic search for an exotic arrival. There are other times when the appropriate policy is to promote from within. Ferguson, like Arsene Wenger, appears to have taken that approach this summer. Ronaldo's exit means Rooney can be elevated.

There was something all-consuming about Ronaldo, the top scorer with star billing, the man who monopolised the free kicks and penalties. Now, whether or not he wants it to be, it is Wayne's World. The No. 7 shirt has gone to Michael Owen, the spot on the right wing to Antonio Valencia, but top billing is Rooney's.

And as the post-Ronaldo era began, it seemed a natural fit. Rooney's blend of inspiration and perspiration brought the only goal, his quest for the man meant he was invariably involved in everything United created. His strike - a second of the season, including his Community Shield equaliser - came when he reacted quickest after his own header, from Nani's cross, had hit the post.

The rebound was converted, yet rewind a few months and Rooney, rather than Nani, would have constituted the supply line from the left. Twelve months ago, Ferguson promised to deploy Rooney in a central role. Now he has no choice. "The golden boy of English football", as Sven-Goran Eriksson called him three years ago, has settled for displaying his steel. Now it is time to show a different sort of mettle.

Rooney has long been a paradox, a man with the talent of a fantasista and the personality of a midfield scrapper. He has attracted eulogies for his unselfishness, his adaptability and his will to win, rather than the sheer level of skill that was astounding upon his emergence at Everton as a 16-year-old. He is a players' player, the sort who seems to think his duties include providing Patrice Evra with cover at left-back, tackling with greater vigour than supposed ball-winners and sacrificing himself for the greater good.

Now others should sacrifice themselves for Rooney. In an otherwise workmanlike United performance, he provided the invention: a dipping shot Joe Hart tipped over, a fierce half-volley the Birmingham keeper parried, a pass with his chest that should have brought Owen's opening goal for his new club.

Ferguson recognised the importance of his strike. "Hopefully that gets him on the road to a very significant total this season, because it's good if you have two or three strikers who get over 20 goals," said the Manchester United manager. "He is capable of that, we know that's not impossible for the boy, so hopefully he will do that."

Whether United's other goalscorers can muster 20 apiece is a moot point. Dimitar Berbatov had a header cleared off the line while Owen, sent clear by Rooney in stoppage time, was thwarted by Hart. By then a Birmingham team who played with admirable resolve could have been level. Evra had produced a goal-line clearance to thwart Franck Queudrue, Cameron Jerome and Keith Fahey both came close and the replacement Christian Benitez drew a superb stop from Ben Foster.

"Fantastic," added Ferguson. "I think he has learnt from last week [in the Community Shield]. It was an unusual, nervy performance. We know he has got ability and he proved that today."

Foster may be kept busy in the next few weeks. Injuries are mounting for United, particularly at the back where Rio Ferdinand sustained a thigh problem in training.

Ferguson added: "I think Ferdinand is out for maybe two weeks. Nemanja Vidic is back in training, which is good news. Hopefully we'll get him fit for Saturday which is Wigan away. Jonny Evans is injured again, Gary Neville has just started training and young Rafael has his dislocation of his shoulder. We're having a hard time of it with defensive injuries over the last two years."

With Fabio da Silva at right-back and John O'Shea as captain, there was an unusual appearance to the United rearguard. In contrast, there could be a familiar look to the sight of Wayne Rooney celebrating a goal this season.

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MAN OF THE MATCH: Wayne Rooney - The greatest tribute came from Alex McLeish. "He's a huge talent, a natural footballer. You get the Zidanes and the Platinis: you see them over the years, they are just naturals," said the Birmingham manager.

MANCHESTER UNITED VERDICT: Traditionally slow starters to the season, they can take comfort from the result and the clean sheet. The sight of Nani starting, as he had done in the Community Shield, suggests Ferguson believes the Portuguese will play a pivotal part this season, but positions in his midfield remain up for grabs.

BIRMINGHAM VERDICT: No points, but plenty of positives for McLeish. Roger Johnson, in particular, had an impressive debut in defence and the promoted team were organised and diligent, rarely affording United the space some opponents grant them. James McFadden's performance on the left flank was a reminder that McLeish appears to know something that has eluded other managers: how to get the best of the mercurial Scot.

ON THE ROAD: Birmingham's boisterous fans were in their element, taunting their United counterparts throughout, though some of their chants were unrepeatable. "See you on the motorway," was one chorus. It brings a new meaning to their usual refrain of "Keep right on until the end of the road".