Sir Alex's side could even afford a missed penalty from Rooney and several spurned chances en route to a fifth straight victory in the Barclays Premier League to go two points clear at the top of the table.
United were slower into stride than in this fixture last term, and yet still led after only eight minutes. David De Gea had been called into drastic action to kick away a Ramires shot early on but the opener soon arrived, in front of the Stretford End.
Ashley Young was fouled and swung the free-kick over for Smalling to bury an unstoppable header for his first league goal for the Reds. Replays showed the defender may have been marginally offside and the goal provoked a decent response from the visitors. When Anderson passed the ball straight to the Spaniard, Old Trafford held its breath but the £50million man dragged his shot wastefully wide of the far post.
De Gea caught a Bransilav Ivanovic header and saw Frank Lampard lash wide, after the England international midfielder rightly escaped a handball shout inside his own area. There was an almighty let-off on 26 minutes when Torres was onside and in the clear but squared the ball. Ramires stretched to force a wonderful, improbable stop from De Gea with Daniel Sturridge waiting behind for a simple tap-in.
The Reds no.1 gathered the resulting corner at the second attempt and also kept out an unmarked Sturridge while Torres sent an unconvincing overhead