's role as a United match-winner in the post Cristiano Ronaldo era got off to the perfect start.
The form of the England striker is paramount if United are to overcome the loss of the £80m World Player of the Year and Carlos Tevez.
Roo has been given licence to thrill by Sir Alex Ferguson by prowling the danger areas more often and not being restricted by the left-wing role that left him relatively anonymous against Barcelona in the Champions League final in Rome.
If this is a sign of things to come, then the England striker is going to tear up the ground and emerge as Ronaldo's match-winning heir.
Rooney has endured some big disappointments after storming into a new campaign. In 2006 he blitzed Fulham with two goals in an Old Trafford opening match but then had to kick his heels serving a three-match suspension for a pre- season red card in Amsterdam. It was another eight games before he scored again.
Two seasons ago against Reading, he was on fire in the first match at home but then his blistering start was abruptly halted when he broke his foot in that match. It was almost two months before he regained his goal sharpness and scored again.
The concern among many United fans is that the champions are only a Rooney injury away from potential disaster having lost Ronaldo's strike output and Tevez's impact play.
Probably the Reds' backroom staff, along with the crowd, sat with their fingers crossed hoping he'd come through this one after his track record.
Ronaldo's goals last season effectively won United eight matches in which he was the lone scorer in a Reds' victory. It secured the champions 18 title points and two European wins against Sporting Lisbon and Lyon.
By comparison, Rooney only managed two match-winners - in the November Manchester derby and against Wigan in January.
But with Ronaldo now in Spain, the door is open for the England frontman to be United's talisman.
He was in irrepressible form against the Premier League newcomers and his personal battle with neighbours City's Joe Hart, who is on loan at St Andrews, was a compelling highlight of this match and an encouraging start to life without Ronaldo for the Reds' hero.
Hart played his part in the duel shrugging off some abuse from United's support for his Eastlands connection. It looked initially like he might have one of those glory days for keepers that frustrates the Reds on a regular basis when he arched backwards to tip over a wonderful 25-yard right-footer from Rooney in the first half.
He was to later get his full body behind a full blooded 35-yard Rooney half-volley. But Hart was all at sea at the defining moment of this game. The United striker stole ahead of Birmingham's defence to meet Nani's 34th minute cross. Hart was still wondering where the ball was when Rooney pounced to stab in the rebound off the post from his own header.
Goal chances weren't exclusively Rooney's but Fergie must have wished he'd have been on the end of the Darren Fletcher opportunity in first-half injury-time when the Scot swiped Evra's cross wide.
United's winter sequence of eight 1-0 victories last term meant a nail-biting mid-season in the Reds' successful title charge and there were moments when Birmingham popped up to scare the life out of Old Trafford most notably when Ben Foster pulled off a 78th minute save from their sub Christian Benitez.
Rooney's mantle as the three-points winner was almost taken away from him when substitute Michael Owen was handed a potential dream debut goal in front of the Stretford End.
Berbatov's replacement blazed away from the Birmingham defence but faced with a one-to-one with Hart, the keeper once again proved he's top notch as his legs steered the newcomer's effort away.
United's inability, on their own manor, to open up Brum was the one topic on the lips of fans streaming out at the end and put a worrying damper on Rooney's exciting starter.