Bertrand felt his side were deserving of victory – never mind a point – until the 77th minute dismissal of Pierre-Emile Højbjerg.
“It's very tough to take," said the skipper, whose second-half opener was instantly cancelled out by Demarai Gray.
“From the performance, there are positives to take. We addressed the situations we needed to from the previous games – we managed to start sharp, right on top of the game and controlling the game. That was the main focus and what we've been working on.
“We need to show more maturity as a team and be more on our toes after we score, because that's when you're most vulnerable – we should all know that.
“We thoroughly deserved to win right up until the sending off, which probably changed the game, but you can't come away with a loss."