Van Persie took his tally at United to 15 goals in 21 games with the opener in Saturday's 3-1 home win over Sunderland. It is on a par with Ruud van Nistelrooy's introduction and means the 29-year-old has now scored an incredible 60 times in his last 72 Premier League games.
"I saw the finish," said Smalling. "It wasn't easy to put it in that top corner but he is a quality player."
For Smalling, the achievement is even more remarkable given Van Persie had barely played a pre-season game before he was pitched into his debut at Everton in August, barely 24 hours after completing his £24million move from Arsenal.
"Obviously he only came in the summer and didn't have much of a pre-season," Smalling added. "But he came straight into the matches and has been such a threat. He is putting teams on the back foot and making our job easier at the back."
Yet, other than the victory that preserved United's six-point lead at the top of the Barclays Premier League, perhaps the most significant event was the return of Nemanja Vidic, following a 16-month injury lay-off, during which time he made only 13 appearances.
Although he was partially responsible for Frazier Campbell's goal with an uncharacteristic failure to clear inside his own six-yard box, Vidic cannot be blamed for a sorry return of only four clean sheets all season.
"There was a bit of carelessness, which is disappointing because we wanted to keep a clean sheet," Smalling said. "Our record with them has not been great and it would have been nice to get one going into the Christmas period."
However, the bonus is that even with such a shaky back four, United have established a healthy position from which they are favourites to clinch a record 20th championship. Yet, as Phil Jones is painfully aware, the situation looked even better six games from the end of last season, but ended on a very different note for United.
"We are in a fantastic position, exactly where you would want to be at this stage," said the former Blackburn man, who was starting a league game for the first time this season. "But last season was my first at United and I experienced something I had never experienced before. I learned that in this league, it is never, ever over."
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