The shrewd acquisition from Arsenal is the Barclays Premier League's top goalscorer but the manager feels it understandably took time for his team-mates to adjust to his style in order to realise his full potential.
The dramatic late equaliser at West Ham in the FA Cup last weekend again illustrated the Dutch hitman's qualities and he is likely to be a man Liverpool will fear in Sunday's big game.
"I said some time ago that I don't think we appreciated the full use of him but I think that's happening now," stated Sir Alex at his pre-match press conference. "We're more familiar with the type of player he is and that's helped us. He's become really important to us.
"What he did last year was only the culmination of a few years at Arsenal. Any player in the first year, you never know for sure. Who'd have thought Wayne would have scored a hat-trick on his debut? That was fairytale stuff. You never know what you're going to get. What we did think is that we'd found a very good player."
The manager feels the club did not pay too much for a player in the final year of his contract at the Emirates Stadium, which certainly looks the case on the return he has already given on the investment, and cited Samir Nasri's transfer to Manchester City as an example of how the market works.
"The first thing we looked at was the player's ability," he revealed. "To pay that amount of money was a lot for a player in his last year. But the thing about that is that it was proved a year before when City played £24million for Samir Nasri - you either want him or you don't want him.