Bryan Mbeumo and Yoan Wissa scored for the Bees, with Ethan Pinnock also putting through his own net.
Glasner later said: "When you lose it is always disappointing in a game like this. We don't look for excuses or complain about anything. it is how it is. We had many opportunities to create chances. When you concede two goals it's difficult because we have to score three. We will analyse it and have more compactness in defense. We are disappointed today.
"We are disappointed but it is how it is. It makes no sense to complain now. We won't get this goal back for a draw. We had a great reaction after the 1-0 at half-time and played well in the second half. We scored but it was offside. We could have avoided the cross for their goal and defended better. I'm very confident that when we get into our rhythm then we will get into these games."
On Marc Guehi's performance, Glasner added: "Everyone can see he is completely focused on Crystal Palace and the game today. The last two days, we didn't speak about transfers because we focused on the game so no news."