A first half strike from defender William Gallas was added to in the second period by two goals from Eidur Gudjohnsen, a Graeme Le Saux effort and our FA Cup dreams are over for another year.
"We shot ourselves in the foot with the goals we conceded, all four," said Glenn afterwards. "We could have averted the first right the way through to the fourth. If you do that in such a big game you're going to pay the price.
"We weren't at our best. I've got to say there were key moments in the game, we hit the post and it might have made it a different game completely.
"We didn't perform well enough to have won the game and Chelsea obviously deserved to win."
Glenn suggested that possibly the boys were a little too keyed up for the cup return with his former club.
"They weren't more committed than us, I think we were over-committed and didn't pass the ball nearly as well as we can. Whether that was a bit to do with the pitch, it is difficult to pass on this at the moment, but we played too long and a bit too passionate, with too much commitment.
"They got their noses ahead and we were then chasing the game. It is disappointing because we didn't play nearly as well as we can.
"I'm disappointed at the way we've given away the goals, that we've been knocked out. But, in a way, I'm disappointed that we didn't give ourselves the best possible chance in the sense of the way we normally play here.
"That was really disappointing and we were possibly too hyped up for the game, if you can be too hyped up."
The boss added that he may have to take the state of the pitch more into account for the remainder of the games at the Lane this season.
"It's not the same pitch it was early in the season and I've got to think about that because it's not going to get any better until it's ripped up at the end of the season.
"That is not an excuse for today's game - we did not deserve to win."
Glenn says that the team paid the price for conceding four goals that could have been averted against Chelsea on Sunday.