Heidar Helguson's third-minute header looked set to be the only goal until captain Mark Hudson threw himself at Aron Gunnarsson's cross with eight minutes to go.
Robert Koren's goal in the 90th minute made the home side sweat in the closing seconds but they held on to maintain their 100 per cent record at the Cardiff City Stadium.
Cardiff have made a habit of starting games well and they scored within the opening five minutes for the third time in their last four games when Craig Noone stood up a cross for Helguson, who nodded home after three minutes.
The chances continued to flow freely for the Bluebirds with Mark Hudson's header rattling the bar and Joe Mason and Gunnarsson also having chances.
The Tigers began to come back into the game as the match headed towards half-time. Koren, who shone throughout for Bruce's men, had a shot blocked and then Sone Aluko's effort went over the bar.
Noone had been in fine form for Cardiff in recent weeks and he was only denied on 55 minutes by the feet of Ben Amos after the former Brighton winger cut inside his marker and lashed a low shot towards goal. A minute later Helguson failed to test Amos when he headed just over when unmarked.
Bruce sent on David Meyler and Robbie Brady but it was Koren who had the next chance, firing a snap-shot wide from 18 yards.
At the other end referee Iain Williamson waved away penalty appeals from the home side after Joe Mason felt he was fouled inside the box. It was then Noone's chance to threaten the Hull backline with two shots in quick succession, the first was blocked and the second was kept out by Amos.
Aluko then came incredibly close to his seventh goal of the season in the 70th minute with a 25 yard free-kick that clipped the bar.
Peter Whittingham then tried his luck from a free-kick only to see Amos to make a sensational save but just a minute later Hudson's flying header set them on course for the three points.
There was still time for Whittingham to hit the bar with a 30 yard free-kick before Koren set up a nail-biting finale with a stunning 25-yard volley.