The Dutchman netted his fifth Premier League hat-trick as United wrapped up their 20th title with a 3-0 victory at Old Trafford.
For the second of his treble, Van Persie ran onto a 50-yard Wayne Rooney pass to fire a first-time volley beyond Brad Guzan from just outside of the area.
"It was goal of the century for me from Robin van Persie," said Ferguson. "It was marvellous - the technique with his head down, over the ball and just perfect timing. It was a magnificent strike.
"He has been unbelievable, his early form was fantastic. He had a dry spell, as most strikers do, but he has come back from that and he was unbelievable tonight."
Van Persie has netted 21 goals in 33 Premier League appearances this season.