Steve Bruce believes his side couldn't have given much more against Manchester City at St James' Park.
His side were 1-0 up and 3-2 up, but could not find a way of holding on as Ferran Torres struck a hat-trick on Tyneside.
Despite a respectable effort, United lost for the 17th time this season and will slip down to fourth bottom again if Brighton beat West Ham on Saturday night.
Bruce said: "We gave it a right good go but when you play against these, defensively you have to better than we were.
"Although I can't remember my goalkeeper making save after save, the sloppiness of conceding so many goals was the disappointment of the whole evening.
"How often do you score three against this mob? Not very often.
"So the disappointing thing is we got up and we were a bit naive.
"For the way, they went about their work I was delighted with them but they weren't quite good enough."
