Both strikers bagged a brace in a routine Premier League victory, with Van Persie turning in another superb performance.
Both Ferguson and Manchester City boss Roberto Mancini feel the Dutchman is the key man in this season's title race - and Van Persie offered more evidence with a virtuoso display.
"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.
"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."
Hernandez took his own tally to 12, just eight short of his stellar first season in England.
"Since Javier came, he has shown he is a penalty-box player," said Ferguson. "He is tremendous. He latches onto things. He is brilliant."
United's defence has been their Achilles heel this season but they achieved a second consecutive clean sheet.
"Don't mention that for goodness sake," joked Ferguson. "Don't tell anybody. No, we're delighted about that."
Ferguson admits he will rest some of his key men in next week's FA Cup tie at West Ham.
"We will make a few changes for the cup tie," said Ferguson. "We took Michael Carrick off as soon as we got the third goal. They deserve a break and they have played in all the games.
"We'll have a look at the situation. We've got plenty of players to freshen it up."