Two times in the second half the ball was lost in midfield and United capitalised to the full to secure the goals that now see them five points ahead at the top of the Premiership.
"Up until nearly 70 minutes we were still in the game - a game that our keeper kept us in," said Glenn. "They opened us up a few times in the first half, in the second we seemed to nullify that well.
"We spoke about it at half-time and it seemed that we were always in the game. The two goals we gave away came from giving the ball away cheaply, both times on the half way line.
"The team, collectively, didn't do enough to avert the goals. We could have marked a lot better both times in the box.
"But they have got so many different players that can score coming from different places - that is perhaps the added dimension they have got.
"I can't fault the effort and workrate we put in though."
Glenn pointed to the fact that surrendering possession cheaply cost us dear on two occasions against Manchester United on Sunday.