Hull twice came from behind to condemn St Helens to a third straight defeat and give their coach Lee Radford a hard-fought victory on his 100th match in charge.
A dour penalty-ridden game finally came to life in the final quarter and the Black and Whites sealed their third win of the season 12 minutes from the end with a rare eight-point try from Carlos Tuimavave before Albert Kelly made sure of a 24-14 success with his second touchdown of the game.
Fresh from back-to-back defeats, this latest setback increases the pressure on Saints coach Keiron Cunningham, although it was a much-improved performance from his side, largely down to skipper Jon Wilkin’s emergency role of scrum-half.
Cunningham reacted to the home defeat by Wakefield by axing young scrum-half Danny Richardson, the man originally chosen to stand in for broken-leg victim Matty Smith.
A potential switch from the pack for Wilkin was described by Cunningham in pre-season as plan Z but needs must and Wilkin has previous experience of helping his side through a playmaking crisis.
Hull enjoyed most of the early play, largely through stand-off Kelly, who opened the scoring on 12 minutes, burrowing his way through the Saints defence after prop Scott Taylor caused problems with an offload just short of the line.
Marc Sneyd added the goal to make it 6-0 and right winger Mahe Fonua would have increased the lead had he been able to take a difficult pass from Kelly but the chance went begging.
St Helens took some time to work their way into the game and they needed a huge slice of good fortune to draw level on 23 minutes.
Hull full-back Jamie Shaul was unable to gather Theo Fages’ high kick and centre Tuimavave, in attempting to clear the danger, merely kicked the ball into the hands of second rower Dominique Peyroux, who will never score an easier try.
Mark Percival’s conversion locked the scores at 6-6 and he put over a penalty four minutes before half-time to give his side the lead for the first time.
Hull had earlier spurned a simple kick at goal and took a more pragmatic option early in the second half when Saints prop Kyle Amor was pulled up for a high tackle and Sneyd levelled the scores with a 50-metre penalty.
The former Salford and Castleford half-back then slotted another penalty to restore his side’s lead after Peyroux had taken him out off the ball.
The game appeared to be slipping away from Hull when substitute Jansen Turgut was sin-binned on 58 minutes for putting his elbow into the face of St Helens prop Alex Walmsley.
Percival kicked the resultant penalty from 40 metres out to draw his side level before taking a pass from second rower Zeb Taia a minute later to cross for a second try and put them back in front.
However, the lead changed hands for a fourth time 12 minutes from the end when Sneyd forced a goal-line drop-out and then produced a sublime pass to get Tuimavave weaving his way to the line.
Sneyd calmly put over the conversion and maintained his 100 per cent record with the boot this season by kicking a penalty from in front of the posts after Walmsley had been punished for a foul in the act of scoring.
Hull were forced into some desperate defence as Saints launched a valiant late bid for victory and they broke away in the final minute to add a further try through Kelly, with Sneyd taking his goal tally to six from six attempts.