The Frenchman has been excellent in recent weeks but could not find a way through against the Gunners.
The defeat left Bruce still fighting for survival although they can seal their place in the Premier League if they beat Leicester City on Friday night and Fulham fail to beat Burnley.
Bruce said: "Allan Saint-Maximin in the last few weeks has produced all sorts of magic but it wasn't quite there today. We've never thought we're safe.
"We have four games left and we still have a lot to play for.
"We didn't play well enough today against a decent Arsenal team.
"We have to regroup, go again and get ready for next week. It was simply that service to [the attackers].
"I think Allan probably played too deep. He was a little frustrated and got too deep."
After the four-match unbeaten run, Newcastle went down to Arsenal and now have to lift themselves for tough clashes with Leicester then Man City.
Bruce said: "We're disappointed because we haven't got near the performances of late.
" Arsenal played well. It's a poor goal after four minutes.
"When you're chasing against these lads it's always going to be difficult. "Arsenal were the better side today it was as simple as that."
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