Smalling helped United secure a vital 2-1 victory at Arsenal on Sunday hours after City moved six points clear of their arch rivals with a last-gasp win against Tottenham.
The defender said: "Soon enough, if we keep ticking these wins then they'll crumble."
Sunday was the first of four away matches Ferguson identified as key to United's title hopes, with trips to Chelsea, Tottenham and City still to come.
Smalling said: "It was a massive win for us. Even at 1-1, we all knew that we really needed to win this game because of what happened earlier, and I think we showed real character."
The result was a third victory in a row for United in all competitions following back-to-back defeats over the new year.
Danny Welbeck has scored in every one of those games - the best run of his Red Devils career - and Smalling claimed there was now no doubting his England team-mate's Premier League and international class.
"If he can keep this form all the way through the year, I think he's going to have a great end to the season and a great summer as well," he said of Welbeck, who is now on the brink of reaching double figures in a campaign for the first time.
"He's come on leaps and bounds. He always had that pace and that finishing ability. But now he's obviously a lot stronger because when he plays up on his own or Wazza's (Wayne Rooney) just off him, he needs to be strong and we can't lose the ball.
"I think that's something that he's really gained and he's scoring goals. He's had a knack of scoring good goals this year and at vital times as well."