The Magpies have been beaten twice in their six games since the Premier League restart, and they've both been at the hands of Pep Guardiola's men, who ran riot at the Etihad Stadium.
It was probably the worst time possible you could have faced City, who were looking for a strong response following their shock 1-0 defeat to Southampton on Sunday.
And a strong response is what Newcastle got, as early goals from Gabriel Jesus and Riyad Mahrez set the hosts on their way to a routine win, with David Silva and substitute Raheem Sterling also finding the net either side of an own goal from Federico Fernandez.
And Bruce, who has earned praise for basically guiding the club to safety this season against the odds, admitted his team had simply been nowhere good enough on the day.
"It was painful, I'm afraid, especially after where we have been, but I think the whole thing has obviously caught up with us and we haven't done enough," said the Magpies boss.
Asked if the result was down to how good City were, or how bad his players were, the Newcastle manager: "A bit of both.
"There's times where you hold your hand up and say you were well beaten, but for me we didn't do enough to make sure it wasn't just that easy for them.
"They're very, very good, we know that. Since the lockdown, they've turned the champions over, so we're not alone, and to play them twice in a week has been difficult, but I expected a bit more resilience than what we put up today.
"We gifted them some goals by giving away cheap possession in wrong areas and against a team like this one, they're going to punish you, and we got punished.
"They were, on the day, just too good for us. Unfortunately today, we were nowhere near the level which we had to get to if you are going to take anything from here."
Newcastle were hurt before the game had even kicked off, with key attackers Allan Saint-Maximin and Miguel Almiron only fit enough for the bench due to injury.
And Bruce said it was too big a task to handle City without his strongest line-up.
"I'm not going to make excuses, but we had far too many of our big players not with us.
"Most of them are injured or they're carrying soft tissue injuries which are difficult to run off. They're not just a knock or a cut. We had six or seven not available today, and when you're coming against this lot it's probably too many.
"But, some of our play was poor. We gave the ball away in bad areas, we didn't do enough defensive, and at times it was too easy for them and that disappoints me."
Newcastle United manager Steve Bruce admitted his side's performance was 'painful' to watch as they were hammered 5-0 by Manchester City.