Sir Alex has explained why he substituted Wayne Rooney despite the centre-forward\'s brace in the victory against Aston Villa. Rooney took his tally for the season to 31 with an early penalty and deflected strike but was replaced by Dimitar Berbatov as Old Trafford celebrated taking a 3-0 lead. Despite his goals, the England international admitted afterwards he wasn\'t satisfied with his performance and the manager feels Rooney is at his brilliant best when playing on the edge, rather than with the side in complete control. \"I think Wayne is the type of player who has to play on the edge in a game really,\" Sir Alex told MUTV. \"When it\'s a really close and competitive game. When it gets to that casual bit, he\'s worse than the rest of them. He gets so casual about it. He\'s better when he\'s right on the edge because he\'s a marvellous player when he\'s right on the edge.\" Danny Welbeck feels his strike partner\'s honesty in appraising his performance shows his winning mentality. \"He’s been on a hot streak all through the season and he keeps banging in the goals,\" declared Welbeck. \"If he’s said he’s disappointed in his own performance, that just shows you what sort of character he is. He’s scoring goals and he’s still not happy. That’s only going to help our team and have a positive effect.\" Another player substituted was Paul Scholes, after another midfield masterclass from the evergreen 37-year-old that included two majestic volleys which almost brought him another sensational goal. \"I know, I\'d have loved one to go in,\" admitted the boss. \"It would\'ve taken the roof off the place. It was a great performance from Paul. He dictates the rhythm of the game and is just a fantastic player.\" Nani\'s goal also brought a smile to Sir Alex as it wrapped up a convincing win and proved he is recovering top form after being sidelined through injury. \"It\'s absolutely brilliant to get him back,\" enthused the boss. \"He can play either side or through the middle and is such a valuable player to have. He\'s been out a few weeks but he\'s back fit and fresh. He\'s a good addition to our squad now.\"