The boss described the firtst half as '11 magnificent performances' as we stormed into a 3-0 lead via Dean Richards, a goal on his debut, Les Ferdinand and Christian Ziege.
But United hit back, responded within a minute of the restart through Andy Cole and went on to win 5-3 through Laurent Blanc, Ruud van Nistelrooy, Juan Sebastian Veron and David Beckham.
Glenn admitted 'you are never sitting comfortably' against United but he was desperately disappointed our first half endeavours counted for nothing.
"In the first half we were very decisive with the way we played," explained Glenn. "We were confident on the ball and nullified them when they had it.
"In the second half we were totally the opposite. We were totally disjointed, went looking for the ball and hunting the ball individually and consequently lost the belief we had first half in ourselves.
"They were the two key elements for us. Both managers can stand here and say it was a Jekyll and Hyde performance but they have the ability and clinical finishing they showed.
"I don't think we were frightened but that early goal in the second half allowed them to have that belief. They've done it before. They nearly did it against Newcastle recently.
"It's not the first time they've done this. You are never sitting comfortably. That's the quality they have in their team."
Glenn said both teams deserved credit. "We deserve credit for the way we played, the goals we scored and how we scored them but you have to give credit to them for how they threw caution to the wind.
"They go and get the goal 45 seconds into the second half and you sit there and know they going to create.
"You aren't sitting there frightened, just wanting to get things back to how they were in the first half.
"In the second half we sat too deep. The reason - because we didn't have enough pressure. Our full-backs didn't search forward enough and force Solskjaer back in the second half.
"Beckham stayed wide so they only had two in midfield and we should have outnumbered them in there but we didn't pass the ball anywhere like we did in the first half.
"It wasn't through complacency. The early goal gave them the belief they needed.
"If it was 3-1 with 20 minutes left we might have been sitting here talking about a victory. But that put them on the front foot.
"They probably thought at half-time that they had nothing to lose and the goal gave them that belief. You know they are a good side and will create.
"We didn't get our game going at all in the second half. There was no flow. On another day you might get the fourth goal and settle down. But that goal in 45 seconds gave them a maasive boost."
Glenn Hoddle looked back on a 'Jekyll and Hyde' display after Saturday's amazing Premiership encounter against Manchester United.