Our American number one produced save after save to keep United and star striker Ruud Van Nistelrooy at bay.
Kasey denied the Dutchman four times in the first half before his resistance was finally broken by Paul Scholes after 68 minutes.
Van Nistelrooy then added his customary goal in injury time to secure the points.
Boss Glenn reflected: "They created some chances in the first half and Kasey was almost playing them on his own.
"To be fair to United they should have been clear in the first half but Kasey was fantastic. It's what he gets paid to do and he came up trumps. He had a wonderful game for us."
After a sterling defensive effort, Glenn was eventually disappointed in the way we conceded.
He added: "At 0-0 after 70-odd minutes you are always in the game but the two goals we gave away we could have done much better defensively in the box. We also gave the ball away cheaply on the halfway line on both occasions.
"I thought it might be one of those games we might actually nick it.
"The lads worked excedingly hard and we were always in the game at 0-0 - even at 1-0 Gus nearly scored for us."
Glenn Hoddle led the praise for Kasey Keller after his magnificent performance against Manchester United.