The German side equalised through their captain, Simon Rolfes, after United had gone into half-time ahead courtesy of Wayne Rooney’s opener, but Robin Van Persie’s superb volley saw United re-take the lead again just two minutes after Leverkusen had levelled.
United never looked back and, despite a late consolation goal from the visitors, they were good value for the three points that kicked off this season's Champions League campaign in fine style.
“If the players don't stick together you don't have any hope,” said the 23-year-old defender. “But we have a very tight knit group here and against Leverkusen we saw that. Even when they scored their first goal, we didn't let our heads drop. We were determined to go up the other end and make them pay, and we did.
“We should have cut out their sloppy goals, then we would have been really happy but overall it was a very good team performance.”
With the first group game of this season’s Champions League safely negotiated, thoughts now turn to next Sunday’s derby and Smalling, pressing for his first start in the Premier League of the season, says the prospect of facing City on their own patch holds no fears.
“It is a game that we all relish. It is better going to their stadium, it is backs to the wall and we will come out fighting.”
Smalling was a second-half substitute when United snatched all three points thanks to Van Persie’s stoppage time free kick on their last visit to the Etihad Stadium, and memories of that dramatic win last December are still fresh in the England