The Swans had numerous chances at home as Renato Sanches made his debut for the club, while former striker Wilfried Bony returned to make his second debut.
Newcastle defender Jamaal Lascelles eventually found the winner for the Magpies and his goal in the second-half proved decisive.
Fabianski made several key saves to keep the scoreline at 1-0 and the Poland international insists the entire squad need to learn their lesson.
He told the club’s official website: “The result has given us a bit of a reality check.
“With our new signings and the atmosphere at the start of the match, you could tell that everyone was up for it.
“But we did not deliver it on the pitch and got punished for it.
“They looked more solid as a team and had some good chances on goal and I feel we probably got what we deserved. The more time we have as a team the more we will click together.
“We have to be aggressive and have to perfect our marking on corners. This is where we need to be getting more of our wins and points. So far we have not been able to do that. We must look to turn things around pretty quickly.
“I am confident we will do that and make the Liberty Stadium our fortress.”