The Red Devils' boss was delighted with the performance of the ex-Crewe player, though was critical of Chicharito's poor penalty
Coming on in the second half, the 18-year-old wasted no time to endear himself to the Old Trafford supporters by firing a low drive from the edge of the box to cap off the emphatic victory.
And Sir Alex has hailed the instant impact, adding that he believes there is a lot in store for Powell.
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"He's going to be a really good player, the boy,” Sir Alex told MUTV. “He's got two good feet and he can strike a ball.”
Powell confessed to being nervous ahead of his debut, but showed calmness and composure to sell the Wigan defence a dummy before burying his effort.
"I was a bit scared when I first stepped out! It was a great feeling to score,” Powell said.
Man Utd looked to have made the perfect start to match as referee Michael Oliver awarded a penalty for a foul by Al-Habsi on Danny Welbeck in the sixth minute.
However, Chicharito’s spot-kick was saved by the Oman international and it would take another 45 minutes of football before United finally opened the scoring, with Sir Alex blaming a slow start on the penalty miss.
“It wasn't a great penalty," Sir Alex continued to reporters. "It can affect you a little bit in the sense you think you're having a good start but have to start again. We had a lot of strikes on goal in the first half without scoring. Danny Welbeck, in particular, had five strikes on goal.”
However, the manager’s counterpart Roberto Martinez was furious with the decision to award a penalty, adamant that Al-Habsi had made no contact with Welbeck, and was critical of a refereeing performance that favoured the hosts.
"He [Welbeck] dived, he dived for the penalty, you'll see it on the replay,” Martinez added.
“The penalty was as bad a decision as you're going to see. It is a shocking decision, in many ways you find yourself fighting against a mountain.
"I've come to United three times now, we've had three players sent off, we just never seem to be measured in the same manner.
"[Welbeck's] last challenge was over the top of the ball, it was reckless, it's dangerous, it's a red card."