England centre Mark Percival and exciting winger Regan Grace scored two tries apiece as Saints overcame injury-hit Hull at the Totally Wicked Stadium – their fourth win of the season over the Black and Whites, who have now lost their last nine matches.
Saints, who handed debuts to former Bradford forward James Bentley and 17-year-old Jack Welsby in the absence of a host of regulars, led only 18-12 at the break but ran away with the game after the break.
Percival had opened the scoring after 10 minutes, supporting a break by stand-off Jonny Lomax, and makeshift hooker Morgan Knowles added a second after fending off two defenders for a soft score.
Danny Richardson kicked both conversions but Jordan Lane jinked his way over for Hull’s first try and substitute Brad Fash added a solo effort to bring the visitors level.
Saints then nudged their way back in front on the stroke of half-time when prop Luke Thompson barged his way over.
Richardson’s third conversion made it 18-12 and he extended the lead with a penalty 10 minutes into the second half.
Saints missed a clear-cut chance to go further in front when Thompson burst clear but ruined the move with a wayward pass to the supporting Barba.
However, Percival made no such error moments later when he broke clear to dummy his way over for his second try.
The final quarter belonged to Grace, who scored his first try in an opportunistic manner from close to the corner flag and raced 60 metres for his second, ducking under full-back Hakim Miloudi on his way to the line.
Richardson made it seven goals from seven attempts to wrap up the scoring.
St Helens: Barba, Makinson, Costello, Percival, Grace, Lomax, Richardson, Amor, Knowles, Thompson, Bentley, Ashworth, Wilkin. Substitutes: Douglas, Lees, Spedding, Welsby.
Hull: Miloudi, Faraimo, Scott, Griffin, Talanoa, Connor, Harris, Taylor, Washbrook, Matongo, Lane, Hadley, Manu. Substitutes: Abdull, Bienek, Fash, Litten.
Referee: Chris Kendall (RFL).