Jean-Philippe Mateta struck the winner for Palace on Tuesday night.
McKenna said: “A frustrating night, probably too many similarities to Saturday for our liking, in terms of a really tight first half.
“Not fantastic in terms of the flow of the game, lots of stoppages, we didn’t manage to create the game we wanted, didn’t manage to create as many opportunities as we wanted, but having said that, neither did the opponent. We were solid, there was very little in the game, very few opportunities at either end.
“Second half, we came out much better, we were in the ascendency, we felt like we could really push on in the game, we got ourselves in a pretty good position and some momentum and then we conceded a really poor goal and in a tight game like today, that ends up decisive.
“We tried at the end to break them down, they were defending and counter-attacking well and we weren’t able to find the solution to break them down.”
On what was said at half-time, McKenna continued: “They’re a really solid team. If you look across the physical strength and the individual quality of their back five, they’re really hard to break down.
“We couldn’t quite get superiority in any individual duel, we got into some good areas but we weren’t able to produce the quality we needed to create a clear chance and both teams probably cancelled each other out a little bit in terms of the system, and we weren’t really able to impose ourselves on them.
“We knew at half-time we just needed to get more intensity in the game one way or another, so we needed to be more aggressive, needed to be more positive, we needed to play forward quicker, even if it wasn’t perfect, but just to create some atmosphere in the game and in the stadium and put more pressure in their final third.
“And we did that at start of the second half, to be fair, and started to get in some more good positions.
“The first half was controlled and solid, but without creating clear-cut chances because they’re not an easy team to create clear chances against. Newcastle have a top, top forward line and I think they didn’t have a shot against them on Saturday. With the back five they’ve got in place now, they’re going to be hard to break down.
“But even taking away clear chances, we didn’t create as much pressure, as much intensity, as much atmosphere in the game in the first half as we wanted.
“And then when the goal went in, the whole dynamic of it changed and you have possession and territory but a solid team who defend well and counter-attack, and with individual quality and the physicality that they have, they’re always in a much better position.”