The KC Stadium strugglers had looked capable of picking up a much-needed victory as they turned in a promising first-half display - Sone Aluko looking particularly dangerous.
However, that good work was undone when Alex Bruce felled former Hull striker Shane Long in the box and James Ward-Prowse stepped up to net his first league goal.
Graziano Pelle added a second to end Hull hopes nine minutes from time.
"It's a crazy game at times," Steve Bruce is quoted as saying by BBC Sport. "We certainly didn't deserve, in my opinion, to get beat 2-0.
"We did enough to warrant getting something out of it. But we gave away a bad goal.
"It was a penalty and we are where we are because of our inability to score goals."
Bruce, though, believes Pelle should have seen red for a "forearm smash" on his son in the first half.
"The one thing that did disappoint me was a yellow card for Graziano Pelle," he added. "I think it warranted a bit more than that.
"If the referee does see the forearm smash across Alex Bruce's face it's certainly a red card. But he's not given it for that."
