The Portuguese winger was the key figure in the Reds' 17th (and Rooney's second) title, scoring 31 league goals in the process.
"We all knew he was capable of [becoming world-class] but he became more mature as a player that season," Rooney told MUTV's Stewart Gardner. "It was incredible to watch. There were times when other players around him did have to sacrifice themselves for him but because he was that good and he was playing so well nobody had a problem with that. It was a team effort to help him achieve what he achieved that season."
The third part of our exclusive interview, with a focus on the 2008/09 season, will be published at 08:00 BST on Monday 10 September.
Wayne Rooney was speaking ahead of the launch of his new book, My Decade In The Premier League , out Thursday 13 September through Harper Collins.