And Powell admitted the performance had caught him by surprise.
He said: "I think a few of the players got ahead of themselves.
"There was an assumption that as we had played well in the last two games that we would again today, but it does not work like that.
"We just expected things to happen, and when it didn't it became very tough.
"Every game is a challenge and you have to be up for it, and that is a lesson we have to learn."
A real bright spot was the performance of Julien Rinaldi, who provided real impetus from the bench.
And the London coach wished a few more had followed that lead.
Powell added: "I thought it was Julien's best performance of the season.
"When he came on he added some real tempo and to be honest I thought he showed the other players what they should have been doing from the off."
The Broncos now look ahead to a televised clash with Wakefield on Saturday, and Powell knows the exact improvement he has in mind.
He added: "We just have to start better.
"We cannot go into games having to score 30 or 40 points to win.
"I am pretty sure there will be a response and I am sure we will come out strong."