Hull coach Lee Radford was delighted to get a victory in his first match in charge after Catalan scrum-half Thomas Bosc missed a last-minute conversion that would have tied the scores at the KC Stadium.
The Black and Whites fought back from 16-12 down at half-time and appeared to have the game won when they led 36-22 but the Catalans struck back with three tries in the last five minutes through Damien Cardace, who completed his hat-trick, Morgan Escare and Zeb Taia.
Bosc would have earned a share of the spoils had he managed to convert Taia's last-minute try but he was off target for the fourth time in seven attempts to leave Hull savouring a 36-34 win.
"They have tried ending my career before it started," Radford joked. "I'm really pleased with the result but there are obviously some issues to fix up defensively."
Australian stand-off Jordan Rankin was the hero for the Black and Whites on his debut, scoring a long-range try and creating two others in a crucial seven-minute spell in the second half, while centre Kirk Yeaman scored twice, taking his try total for the club to 157 and climbing to fifth in the all-time list.
"We didn't have any football in the first half and I was confident if the penalty count levelled itself up and we got our share of possession, we would cause them problems and we did for the first 20 in the second half," Radford said.
"For whatever reason, we capitulated in that last 20. It gives us something to work on on Monday, that's for sure.
"Any week we'll take the two points but we want to get some consistency in how we defend.
"I thought all the new boys did a real good job. Jordan is a running threat. He likes the football in his hand."
The Catalans were on course for their first win at the KC Stadium since 2008 after dominating the first half but coach Laurent Frayssinous was alarmed at the way his side collapsed after the break.
"It would have been nice to come back with one point but there are a lot of things to talk about on Monday morning," Frayssinous said.
"I am focused more on the performance than the scoreboard. That's why I'm disappointed and frustrated. In the second half we went away from the game plan and defensively we made some soft and poor decisions."
The Dragons could have a disciplinary headache looming after French international forward Olivier Elima was placed on report for a late tackle on Hull hooker Aaron Heremaia which incensed his team-mates.
Radford said: "My eyesight is the worst on the planet but, If he has gone in to roll his ankle, that's a cowardly act and our boys have every entitlement to run in as they did. The game is tough enough, we don't need incidents like that."
Frayssinous said: "I didn't see it live, I need to watch it again."