Despite seeing England international Jake Connor stretchered off with a leg injury in the first half, the East Yorkshire club, already missing a raft of talent, produced a stirring display to initially give their stellar opponents cause for concern.
Indeed, two tries in four minutes from Jansin Turgut and Albert Kelly at the start of the second period actually put them 18-10 ahead against a side who have still not been beaten in three months.
However, the lead did not last long against a Saints team who also knocked them out of the Challenge Cup last month.
Despite a mixed evening by his own high standards, Ben Barba, typically, came up with his second try and 25th of the season to get Saints right back in it.
Then dynamic stand-off Lomax showed his class with two opportunistic scores to turn an absorbing game on its head again.
First he arrowed in off James Roby’s short ball after Hull missed a golden chance to reclaim possession and then – after Morgan Knowles came up with a crucial tackle to deny Hull’s Jack Downs a try – he benefited from Roby’s guile once more to put them 24-18 ahead in the 65th minute.
Hull still had time but lacked the requisite poise and, when Danny Houghton lost possession on halfway, Adam Swift raced in untouched from 50m out, Luke Thompson adding Saints’ seventh try at the death.
Few people could have thought Three Lions could ever have been sung with such gusto so soon after England’s painful World Cup exit.
However, with a little alteration, Hull’s delirious fans managed just that as they sang “He’s going home, he’s going home, Barba’s going home” after the Australian full-back was ‘sacked’ behind his own posts for a drop-out that led to Turgut’s try.
Man of Steel favourite Barba then missed an attempted intercept of Kelly’s fine floated pass and Turgut romped in.
When Dean Hadley – impressive at loose forward – then surged clear from Houghton’s pass on halfway, Kelly got in himself, evading Louie McCarthy-Scarsbrook attempts at rushing him and then charging over the beleaguered Barba.
However, there’s a reason everyone thinks Barba is going home to the NRL – because he is so good – and that showed when he eased over to get Saints back on course for a 12th successive win.
The 29-year-old certainly had the last laugh.
Granted, the eventual scoreline was harsh on Hull who were well-served by Scott Taylor, the England prop whose opening 26 minute spell was as good as anything you will see this season.
Hull – with stand-off Jordan Abdull looking assured on his return from a broken leg – made a lightning start to the game with Bureta Faraimo going over for his first try inside just 56 seconds.
Kelly instigated it on halfway, finding Connor whose swift pass sent the winger away.
He still had plenty to do, mind, yet went around Barba with comparative ease, leaving the Australian star berating himself for such a shoddy defensive effort.
Turgut almost muscled over soon after and, with Taylor leading from the front and Kelly dictating, it was Hull who looked like a team playing on an 11-match winning run.
Saints, in contrast, were often sloppy in possession illustrated best when they spilled on the second tackle after Danny Richardson had performed a 40/20 kick.
Faraimo, though, had shown the frustrating side to his game there, allowing the kick to roll into touch, seemingly unaware of the danger.
His side were let off the hook but not when they coughed up the ball themselves in the 17th minute.
Admittedly, Hadley seemed to have done so backwards when trying to offload but Saints made the most of the possession, Barba applying the silky final short pass to send new England cap Tommy Makinson through from 15m out.
Barba’s mixed night continued, however, when he dropped the ball in the shadow of his own posts after claiming Abdull’s high kick.
Connor picked up the pieces and dived over only for referee Liam Moore to award Saints the scrum, apparently deeming Abdull had knocked it forward out of Barba’s grasp.
Typically, it was Barba who then put Saints ahead soon after, strolling over from a scrum after Jack Logan had failed to deal with Richardson’s steepling kick.
Connor departed in agony in the 33rd minute after suffering an injury when attempting a tackle but it did not deter his colleagues.
Barba was bundled into touch after a kick and Faraimo finished off his second of the night – and ninth in the last five games – by claiming Kelly’s long pass.
Hakim Miloudi, who took over kicking duties, could not convert but Barba was called upon to deny Kelly just before the break as Hull continued to threaten.
Their best work came after the break – but, unfortunately, Saints’ was even better.
Hull remain in fifth and head to Wakefield Trinity next.
Hull FC: Miloudi, Faraimo, Connor, Tuimavave, Logan, Kelly, Abdull, Taylor, Houghton, Green, Turgut, Minichiello, Hadley. Substitutes: Paea, Matongo, Lane, Downs.
St Helens: Barba, Swift, Makinson, Percival, Grace, Lomax, Richardson, Amor, Roby, Thompson, Peyroux, Taia, Wilkin. Substitutes: Fages, McCarthy-Scarsbrook, Douglas, Knowles.
Referee: Liam Moore (RFL).