Both strikers netted twice as the Red Devils ran out 4-0 victors at the DW Stadium on New Year's Day, a result which ensured United remain seven points clear at the top of the Premier League.
And the 71-year-old has now praised the pair, singling out Van Persie in particular as a man at the peak of his powers.
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"Robin is a completely rounded footballer with his ability to make and take goals. His first goal was an absolutely magnificent bit of football, with his balance in turning defender and then, no drawback, he just side-footed it into the net. It was a really good goal.
"We knew we were getting a top player, a major player, who was going to make the difference to the team. Those were my thoughts when we went for him. I knew he would make the difference because he's got maturity, great international experience and he's played for Arsenal for seven years.
"He's come to us at the very peak of his career, which we're delighted at."