The 22-year-old was outstanding as he took on the challenge of playing at right-back for the first time and appeared undaunted by taking on Ryan Giggs head-to-head in front of 67,000 fans.
It's to Simon's credit that Giggs was quiet all afternoon - and eventually substituted - as United relied on Ruud Van Nistelrooy's penalty to take the points.
Boss Glenn explained: "We worked with him mentally and he needed a bit of reassurance that he could play in the position.
"I thought defensively it wasn't his natural game but he is very cute and it showed what a good player he is, playing at Old Trafford against Ryan Giggs.
"I told him to enjoy the game. That was important, how he approached it and he went out there and was very positive with the ball and defensively.
"We worked on a few things, talked him through positional sense in the week but has that ability, went out there, adapted and showed how he's grown as a player, a player who can play in a number of positions for us."
Glenn Hoddle says Simon Davies' performance at Old Trafford underlines how he has grown as a player.