The Red Devils have scored 21 goals so far in the Premier League on the way to second place in the table, having won six of their opening eight fixtures.
However, Jose Mourinho's team came in for some criticism for the approach they took to last weekend's 0-0 draw with Liverpool at Anfield, the first time they failed to score in the league this season.
Defending his manager, Smalling told Sky Sports News: "You can see that we have attacking players, albeit they still have to defend when Liverpool have those attacks.
"But we kept it tight and we know that when we get those chances, more often than not, when we keep a clean sheet or are defensively sound, then nine times out of 10 we will win that game because not many teams can stop us from scoring.
"More often than not, we are the team that is on the front foot, because we are the one with the ball and we have to keep passing it side to side and finish them.
"And more often than not, when we get a goal and go 1-0 up and then the other team has to come out, that is often when we score the second, the third and the fourth. And we have killed teams in the last 20 minutes. But the onus is on us to have to break those teams down."
Up next for United is a Premier League trip to Huddersfield Town on Saturday.