Man Utd's Giggs prepared "two weeks" for Chelsea masterclass
"Honestly, Ryan was fantastic," praised Sir Alex on MUTV, before revealing, "I kept him particularly for this game, I rested him.
"I told him two weeks ago he and Darren Fletcher would play against Chelsea. I thought this game was made for them, given Ryan's ability to hold the ball and beat a man in midfield with that left foot. Ballack couldn't live with him really.
"It could have been a mistake - it's very easy to make a mistake when you've got a squad of 23 players. Genuine mistakes of course because you want to pick a team that wins and the supporters understand that. But today it worked and I'm glad it did."
Giggs was unjustly denied an assist during the game when Cristiano Ronaldo's header, from his cross, was disallowed by the officials. It followed a clever corner kick when Wayne Rooney quickly put the ball down in the 'd' and then rolled the ball into play for Ryan to collect - unfortunately without it being seen by the linesman.
"We've worked at that," revealed Sir Alex. "When you work at it and it's disallowed because the linesman's not watching... Wayne clearly put the ball inside the little 'd' and Ryan noticed it, he took the ball in towards goal - why else would he take it in?
"Fortunately we managed to score from the next corner."