"I thought we looked a threat when we equalised," said Bruce, referring to Ciaran Clark's 65th-minute header.
"Of course Leeds are always going to ask you questions the way they play, they do it very well, but we've gifted them the two or three goals at the end. Unfortunately, they're something which you see on a park on a Sunday.
"We can't make those mistakes we've made here. At the wrong time we've given away poor goals, not defended well enough and got punished. It's unacceptable."
With reference to the failed penalty appeal, the Magpies boss added: "I honestly was all for VAR when they brought it in to make sure the clear and obvious mistakes that the referee misses, that's what the VAR is there for.
"If anybody looks at the challenge you understand that it's a clear penalty. We might not have gone on to win the match but certainly when you take the lead in the Premier League then the outcome could be very, very different."