The strike duo were recalled for the short trip to the DW Stadium after starting on the bench against West Brom and shared the goals in the 4-0 triumph, ensuring it was a difficult afternoon for the home defence on New Year's Day.
In the continued absence of Wayne Rooney, the pair's performance in tandem provides options for the boss with Danny Welbeck also coming off the bench to contribute by assisting the final goal.
"Chicha, as we've known since the day he came, is a penalty-box player," Sir Alex informed MUTV. "He's tremendous in the way he latches onto things and reacts to things brilliantly.
"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."
Veteran Ryan Giggs, also impressive at the DW Stadium on Tuesday, was quick to offer his own words of praise to van Persie for another stand-out performance by the Barclays Premier League's leading goalscorer.