Richard Agar's second stint as the caretaker coach of Hull started with defeat, but not one that should damage his chances of landing the job full time.
Hull competed with commendable spirit but, with their first choice half back missing and Shaun Berrigan forced off early with a shoulder injury, they could not match Saints' clinical finishing.
"We put an awful amount of effort into the game, but we came up with some wrong plays," said Agar, under whom Hull won four of their five matches when he was in temporary charge two years ago.
If Hull sometimes were short of guile, they could not be faulted for grit and determination.
After going behind to a try by Jon Wilkin, put through a huge gap by James Roby, they produced some heroic last ditch defence, notably from Willie Manu, who brought down Lee Gilmour with a candidate for tackle of the season and then dragged the ball out of Roby's hands as he was about to score.
Neither Manu nor anyone else could do much about Saints' second try, created for Stephen Tyrer by superb handling from Leon Pryce and Matt Gidley, but Hull did not let that deflate them.
Perked up by the introduction of Jamie Thackray, they grafted their way back into the game by half time, thanks to a bizarre try.
Gareth Raynor leapt to catch and throw back Tommy Lee's kick. Kirk Yeaman did not seem particularly interested, but Sean Long lingered longer and the Hull man finally toe poked the ball through to score almost as an afterthought.
It was the turn of St Helens' defence to be tested after the break with Hull spending most of the third quarter on the attack without being able to cross the visitor's line.
The sequel to that was predictable. A couple of penalties moved Saints into the danger area and they struck immediately, via Long's ball to Pryce. A Long penalty made the victory safe for Saints, on a ground where they have often found life difficult, moving them back to within six points of Leeds at the top of the Super League table.
Hull's defiance was summed up by Craig Hall's interception and Raynor's try 100 metres away in the opposite corner in the last minute. It was too late to make any practical difference, but it was one of a number of hopeful signs for the immediate future.
Hull: Byrne, Sing, Hall, Yeaman, Raynor, Washbrook, Berrigan, Dowes, Houghton, Cusack, Manu, Tickle, Radford. Substitutes: Thackray, Lee, Carvell, G Horne.
St Helens: Wellens, Tyrer, Gidley, Talau, Meli, Pryce, Long, Cayless, Roby, Graham, Gilmour, Flannery, Wilkin. Substitutes: Cunningham, Hargreaves, Bennett, Fa'avalu.
Referee: R Silverwood (Mirfield).