Cristiano Ronaldo's second-half strike gave Manchester United a fifth successive Premier League win after a 1-0 triumph at Birmingham.
But 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 settled the issue six minutes into the second half and United have now kept five successive clean sheets in the competition.
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.
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.
Ronaldo struck in the 51st minute after a defensive error from Franck Queudrue.