By spending £27million to lure Rooney to Manchester United from the team he supported as a boy in 2004, Ferguson never had any doubts over Rooney's potential.
Yet there have been times during the intervening years when the 24-year-old did not appear to be developing as planned, especially compared to Cristiano Ronaldo's meteoric rise.
World beater: Wayne Rooney is in the midst of his most successful season
But, after dragging United along virtually single-handed for most of the campaign, Rooney's team-mates have come to his assistance in recent times, improving the Red Devils' performances to such an extent that their star man has been catapulted into the elite group alongside Ronaldo, Kaka and Lionel Messi.
'Over the last month or so his game has just taken off,' said Ferguson. 'Confidence has something to do with it of course but he has been in absolutely incredible form over the last few weeks.
'Before, we said that his goalscoring tended to come in bursts. Now he is far more consistent and goalscoring is the area you always want to be judged as a striker.
'It is the area of biggest improvement and with him doing that you have to put him in the same bracket as all the best players. The evidence is there.'
Ferguson is refusing to budge from his target of 30 goals for Rooney, which, while a significant figure, seems a conservative aim given the England forward's double at the San Siro on Tuesday took him to 25.
Rooney will certainly be desperate to add to his tally on Saturday.
Once a Blue: Wayne Rooney burst onto the scene as a teenager at Everton
Despite growing up with Everton posters plastered all over his walls and still keeping a close eye on events at Goodison, Rooney has never been forgiven by the Toffees faithful for abandoning them so early in his career.
At one point he was even abused by a sponsor's wife, such is the fervour Everton fans retain for their dislike of Rooney.
'He always gets a rough ride there although he is probably used to that now,' said Ferguson. 'There is a special motivation for Wayne to do well against Everton but we couldn't have him in better form really and it doesn't matter where we are going.
'He has been the main player. Without a doubt he has been the star for the last few weeks.
'He is in such good form we are going there in great confidence.'
Ferguson will expect Rooney's hunger to filter all the way through a squad that will elevate Antonio Valencia to a starting slot after a couple of eye-catching cameos recently, including crossing for Rooney's first goal on Tuesday.
'We gave Valencia a break because it is his first season at Old Trafford and we don't know everything about him,' said Ferguson. 'He was doing so well for us beforehand and now he is fresh.
'He has come on in the last two games and done exceptionally well so, with Nani suspended, he will start.'
Back in the fold: Anderson (left) and Nemanja Vidic are both in the squad
In addition to Nani, United are also missing Rio Ferdinand through suspension. But Anderson is available after a reserve-team outing last night, while tough-tackling defender Nemanja Vidic is also included.
The Serbian has yet to make an appearance during 2010 after suffering a nerve problem in his leg, leading to claims that he may well be on his way out of Old Trafford this summer, something both the player and his manager have been at pains to deny.
His return is certainly welcomed given Ferguson feels tomorrow's trip represents one of the key games for United, who trail leaders Chelsea by a point thanks to the Merseysiders' victory over Carlo Ancelotti's men nine days ago.
'We have a good record there,' observed Ferguson. 'Maybe the atmosphere does help us because it is a real football stadium.
'Goodison Park is an old ground but it has got the football tradition still attached to it. The crowd are always very noisy and they will make that noise felt.
'But we have experienced that many times before. It is a massive game for us, we recognise that. Beating Chelsea shows Everton's potential, so if we could get one, a positive result would be very important.'
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