The Premier League side took on lower division Blackburn Rovers, and came away with an ugly 1-0 win.
Newcastle were on the back foot for much of the game, but did just about enough to move on to the third round of the cup.
Bruce said after the game: "We have another game on Sunday.
"We will have had six games in two and a half weeks.
"That game last night has made sure some of them have got football in their legs.
"We aren't going to say anything other than we were fortunate."