Manchester City manager Roberto Mancini yesterday expressed his fear that the failure to land Van Persie will prove pivotal in the title race.
And Van Persie offered more evidence to back up that theory with a double in United's 4-0 win over Wigan at the DW Stadium that takes his tally for the season to 19. The first goal in particular was a gem, as he took Javier Hernandez's square ball before stepping inside Ivan Ramis and then belting a superb shot into the corner with his supposedly weaker right foot.
"We knew we were getting a top player who would make a difference to the team," said Ferguson. "That is why we went for him.
"He's played for Arsenal for seven years and he came to us at the very peak of his career. His ability to make and take goals is fantastic."
Van Persie's contribution was matched by that of strike partner Javier Hernandez, who took his own tally to 12, just eight short of his stellar first season in England.
The victory completed an impressive 10-point haul for United from their four festive games and they even managed to keep a second consecutive clean sheet.
United remain seven clear of Manchester City and without some kind of injury affecting Van Persie, it is difficult to see the Red Devils squandering their advantage in the same way they did 12 months ago.
Ferguson is taking every precaution, and that means resting key men for next week's FA Cup tie at West Ham.
"We will make a few changes for the cup tie," said the Scot.
Meanwhile, Ferguson says there is no likelihood of an imminent managerial vacancy at Manchester United.
With Pep Guardiola due to end his post-Barcelona sabbatical next summer, Jose Mourinho tipped to leave Real Madrid, two of the major candidates to replace Ferguson could be available at the end of the season.
It has led to suggestions Ferguson, who celebrated his 71st birthday yesterday, will call time on his United career, which now extends beyond 26 years.
However, the Old Trafford makes it clear he is going nowhere.
"I'm hoping to stay on for a bit of time," he said.