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.
Sir Alex Ferguson's men watched the City-Spurs game in the Emirates Stadium dressing room and, rather being dispirited by the result, they took up the gauntlet to move back within striking range.
Smalling 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."
Yesterday 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.
"Last year, he did well (on loan) at Sunderland and this year he's getting his chance."
The same happened to Smalling last season but he has needed to be more patient this term, at least in terms of playing in his favourite centre-back position.
But with Nemanja Vidic and Rio Ferdinand both injured, his return from a recent bout of tonsillitis has been good for both player and club.
"It's nice to come back into the centre," Smalling said. "I've had a frustrating last month with the illness etc.
"But I'm feeling fit as a fiddle now and hopefully I can have a good run until the end of the season."
Smalling emerged unscathed from a bruising game yesterday, which was something of a throwback to the United-Arsenal clashes of the previous decade.
Phil Jones left the field on a stretcher with ankle ligament damage that could rule him out for the best part of a month, Nani boarded the team bus wearing a protective boot, Rooney limped out of the stadium, Michael Carrick tweaked a hamstring and Patrice Evra suffered a head knock.
United were already without Ferdinand, Anderson, Tom Cleverley, Ashley Young, Michael Owen and long-term absentees Darren Fletcher and Vidic.
Smalling said: "It is obviously bad luck.
"Whoever comes in, we're staying strong. We're not going to moan about it - we're just going to carry on."
United may need all their mental toughness on Saturday when they travel to Liverpool in the FA Cup - their first trip to Anfield since the Evra-Luis Suarez racism row.
Smalling shrugged off the prospect of playing in what is bound to be an even more hostile environment than usual.
"To be honest, we've not really thought about it," he said. "The manager spoke before that we've got five or six massive games coming up and I think he just wants us to enjoy it.
"That's what I'm certainly going to do.
"It'll be nice to do them on their own patch, just like we have done (to Arsenal) here."
