The 23-year-old defender believes the return to full strength for the Red Devils' defence has been key to their form as they increased the gap at the top of the table to 15 points
In 2013, the Red Devils' defence has secured seven clean sheets in 16 games and conceded 12 goals, as opposed to their form before the turn of the year, where in 28 games they kept just four clean sheets and conceded 40 goals, while David De Gea has not conceded in 537 minutes of Premier League action.
Smalling, who has had his starts for the first-team diminished by injury, believes the return of all their defensive personnel has played a major part in the club's performances and form, with the 1-0 victory over Reading allowing them to open up a 15 point gap at the top of the table.
"That's linked in with all our defenders coming back now," Smalling told the club's official website. "It's just Phil [Jones] who is struggling but I think he will be back soon and our strength is shown by the players that we have available.
"It wasn't a pretty game [against Reading]. It got pretty ugly in the second half and I think we were just happy to get the three points. That was what we needed and we got a clean sheet as well so we're happy with that.
"We knew what we had to do before City played, but [City losing 2-0 at Everton] gave us an extra incentive. We would like to have scored a few more goals but we stayed solid and got the 1-0 win."