Hull travelled to the Stadium of Light in the Premier League relegation zone and seeking a first victory in 11 top-flight games.
That run had put pressure on Bruce, who was up against the team he managed between 2009-11, and despite falling behind just 29 seconds into the contest, goals from Gaston Ramirez, James Chester and substitute Nikica Jelavic secured a deserved win.
"We could have buckled after conceding an early goal, but the players have showed great spirit," Bruce said. "Our second-half display was arguably as good as we've seen this season.
"We're a newly promoted team that's been in the Premier League for 18 months.
"It's always nice to win here – with the stick I get it's a little bit sweeter than if you get beat – so it's a sweet Boxing Day."
Bruce attributed Hull's disappointing recent run to absentees, but expects the result on Wearside to get their season going.
"We've been blighted by a little bit of lost form and injuries," he said. "Some of the injuries are long-term but hopefully this result will give us a huge lift.
"We've got a huge game up next against Leicester City. I still believe we'll finish above where we did last year."
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