Michael Owen scored twice in the second half and Park Ji-sung also got on the scoresheet before Scunthorpe United claimed the second goal they deserved in injury-time from the impressive Martyn Woolford.
Related ArticlesScunthorpe 2 Manchester United 5Liverpool 2 Northampton 2; 2-4 pensAston Villa 3 Blackburn Rovers 1West Bromwich Albion 2 Manchester City 1Wigan Athletic 2 Preston North End 1Chelsea 3 Newcastle United 4"It's always going to be a tricky test coming to places like this," Ferdinand said.
"There was great support tonight from both sets of fans but when we got our foot back in the game we settled and started playing and put the game to bed.
"Any game is good to be playing in, I'm just happy to be playing."
Asked about his defensive partner Smalling, Ferdinand added: "Chris is willing to learn, he's hungry, you can see the desire in him.
"He's doing well and taking everything in in training."
With Sir Alex Ferguson watching next week's Champions League opponents Valencia, assistant Mike Phelan took charge of the third-round tie.
He said: "We put a big value on the Carling Cup. We've never set out to demean the Carling Cup. We're holders, we've done that two years in a row and you can see from the players' attitude that we want to keep hold of it."