Chris Smalling believes Manchester City will "crumble" under the pressure if Man United keep up their pursuit of the league leaders.
Smalling played in United's 2-1 win at Arsenal which kept them within striking distance of their Manchester rivals, after City defeated Spurs in Sunday's early game.
And the defender believes big-spending City will collapse if United keep winning.
The 22-year-old told the Manchester Evening News: "Soon enough, if we keep ticking these wins then they'll crumble."
The victory was the first of four away matches manager Sir Alex Ferguson says United must win, with Tottenham, Chelsea and Man City the others.
"It was a massive win for us," said Smalling.
"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."
Another youngster to become a Man United regular this season is 21-year-old Danny Welbeck, who scored the 80th minute winner against Arsenal.
And Smalling was full of praise for his international team-mate, who has scored in his last three games.
He added: "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'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."