A Dimitar Berbatov hat-trick plus goals from Ji-sung Park and Antonio Valencia ensured United maintained the 100 per cent league record against the Latics and helped make another big dent into City's superior goal difference.
"As I said some weeks ago, somebody was going to suffer," Sir Alex told MUTV. "We're really hitting good form now and there's a real goal threat about us from all departments.
"If we're top of the league or joint top with City by New Year's Day I'll be happy."
The United manager also paid tribute to Berbatov after another excellent treble from the Bulgarian.
"It was the right game for him. I needed his height for set-pieces against us and he's weighed in with a hat-trick. We're really pleased for him and it helps with confidence," said Sir Alex.
"Dimitar hasn't had the best of starts to the season in terms of selection given the options I have with Welbeck, Rooney, Hernandez, so I'm really happy for him."