Final Score Manu 1 Birmingham 0
Cristiano Ronaldo's first goal of the Barclays Premier League campaign secured a fifth successive league win for Manchester United at St Andrews as Birmingham succumbed 1-0.
Empics
Liam Ridgewell hunts down Wayne RooneyBut his side were pushed all the way by Steve Bruce's battlers before climbing back into second spot - two points adrift of Arsenal, who also have a game in hand.
Ronaldo, in what was his 100th league start, settled the issue six minutes into the second half and United have now kept five successive clean sheets in the competition since losing the Manchester derby.
It was also their fourth 1-0 league win of the campaign and they have achieved their lofty position in the table despite scoring only seven times in eight games.
• Fergie pleased to pass tough test
But Birmingham can consider themselves unfortunate not to have claimed a share of the spoils and were the more threatening side in the opening 45 minutes.
United seemed nervous at the back during the first half apart from a majestic performance by Rio Ferdinand.
The irony of the outcome would not have been lost on Bruce after Blues were heavily criticised for a defensive performance in earning a goalless draw at Liverpool last weekend.
On this occasion, his side caused the Red Devils all kinds of problems. Olivier Kapo and Gary McSheffrey created several good chances - but ended up with no reward.
Birmingham made an enterprising start and United keeper Edwin van der Sar was twice called into action in the first two minutes.
A mistake by Paul Scholes allowed Cameron Jerome a free run at the United goal and his fierce left-footed drive from 20 yards out was turned around the post by the Dutchman.
Then Van der Sar had to react smartly to cling on to Franck Queudrue's glancing header from the resulting corner by Sebastian Larsson.
The first real threat to the home side came when a long clearance from Van der Sar found its way to Wayne Rooney in plenty of space to the right of the Blues box.
The England striker tried to chip Northern Ireland keeper Maik Taylor, but he had come racing off his line to narrow the angle and managed to block his attempt.
Queudrue became the first player to be booked for a challenge on Ronaldo.
Rio Ferdinand came to United's rescue after 17 minutes when he cleared a downward header from Gary McSheffrey off the line from Larsson's cross.
Ronaldo was causing Birmingham problems and one shot from a narrow angle flew straight at a relieved Taylor after good play by Giggs and Brown.
A misplaced clearance by Van der Sar, when well off his line, flew straight to the lively Jerome.
The former Cardiff player tried to make the Dutchman pay for his error, but he failed to get enough height into his shot and Michael Carrick was able to make the block.
Taylor anticipated a pass from Rooney into the path of Ronaldo and saved bravely at his feet, but Birmingham deserved to be on level terms at the break.
United were forced into a half-time substitution with Van der Sar apparently still troubled by the first-half ankle knock and replaced by Tomasz Kuszczak.
After 51 minutes, Ronaldo broke the deadlock with his first league goal of the campaign.
There seemed little danger when Ferdinand played the ball forward just inside the Blues area, but Queudrue hesitated when he should have cleared and Ronaldo took full advantage. He surged forward and coolly took the ball around Taylor before firing home.
Birmingham tried to retaliate and Kuszczak needed two attempts to gather a low volley from McSheffrey.
But the former West Brom keeper made an excellent save to turn another McSheffrey pile-driver around the post after it took a deflection off Ferdinand.
McSheffrey was only just off target with the resulting inswinging free-kick from a narrow angle.
Ronaldo could have settled the issue but dragged his shot just wide and in the last few seconds Kuszczak kept out a drive from Blues substitute Garry O'Connor.
Fergie pleased to pass tough test
United boss Sir Alex Ferguson admitted his side were outplayed for the first half and believes his men were handed their sternest test so far this season.
He said: 'I thought the first half Birmingham were the better team, full credit to them.
It was the hardest game we have had so far this season. They made it very difficult for us, going in 0-0 at half-time I was very happy with that.
'In the second half we had a better threat going forward and we defended much better.'
Ronaldo's goal proved the difference between the sides and the Scot praised his winger for keeping his cool under pressure.
'He showed composure, he's got the pace to go by people and he took it very well,' he added.
The Red Devils manager sees signs of improvement in his side, who have won four of their last five league games by a 1-0 scoreline.
'I think we are getting together as a team again. You could see that today, the movement was very good and (Wayne) Rooney, (Carlos) Tevez and Ronaldo were big threats. (Louis) Saha is getting there, he is such a threat when he gets on.
One piece of bad news for Ferguson was a toe injury to keeper Edwin van der Sar, and the United manager admitted the Dutchman will not feature in Tuesday's Champions League game with Roma.
'He has a toe injury,' Ferguson said. 'I don't think he will be fit for Tuesday, young Tomasz (Kuszczak) came in and did very well, he will play on Tuesday.'
Birmingham manager Steve Bruce was heartened by his side's efforts in the 1-0 Barclays Premier League loss to Manchester United, insisting he had the best side of his six-year reign at his disposal.
A defensive slip-up by Franck Queudrue gifted Cristiano Ronaldo the chance to score the only goal of the game - an opportunity the Portuguese accepted deftly.
But Bruce refused to see the down side, insisting it was a game of positives for his team.
'I don't think we'll ever have a better chance (to beat United) and in the first half we had to take one of our chances,' he said.
'An individual mistake, a bad mistake cost us the game.
'A draw would have been a great result for us but it was the manner in which we played (which was pleasing).
'Against one of the big, big teams it was as good a performance as we've put in.
'I've got the makings of a good young team.
Bruce added: 'There were a lot of positive in the way we played, the way we passed the ball, the way we competed with them.
'I'm very optimistic. In the six years I've been here this is as good a side as I've had.'