Manchester City manager Roberto Mancini has 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.
"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 went on: "Robin is a completely rounded footballer. He has great international experience, 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.
"His play for his first goal was absolutely magnificent, his turn, his balance, no drawback, just side footed it in. It was a really good goal."
Wigan boss Roberto Martinez conceded his team were beaten by the better side, with the Latics lacking sufficient strength in depth to cope with a run of four games in 11 days.
"It was very unfair to play against the league leaders in a period like that," he said.
"We didn't have the legs or the reaction and you have to congratulate Manchester United.
"They had the luxury of making changes and Van Persie and (Javier) Hernandez looked brighter and sharper. In the end it was a mismatch."