Justin Holbrook’s side opened the scoring after just 90 seconds and were never in trouble as they eased to a 26-4 success.
Super League’s top try-scorer Ben Barba ran in his 18th and 19th of the season for Saints while their long-serving hooker James Roby clocked up a career century of tries after 14 years with the club.
It was a tough night for Rovers, who remain second from bottom, though they did at least rally after a horror start which saw them trail 12-0 after only eight minutes.
The Robins’ kick-off went out on the full and from the penalty, Saints rolled forward and moved the ball right for centre Ryan Morgan to score a try which Danny Richardson converted.
Roby helped himself to a simple try from dummy half after Kyle Amor was tackled inches short. Richardson, who has registered points in his last 19 games, again kicked the goal.
The league leaders had two tries disallowed before they finally got over for a third. Theo Fages and Zeb Taia combined brilliantly to get Barba over and Richardson again goaled.
As the half-time hooter sounded, Barba set off on a mazy 70-metre run and kicked ahead but Tommy Makinson’s valiant full-length dive was in vain as the ball agonisingly rolled dead.
The half-time team-talk of Robins coach Tim Sheens clearly had an effect as they registered their first points of the game within two minutes of the restart. Winger Junior Vaivai followed up his own kick and touched down in the corner but Ryan Shaw was unable to kick the goal.
But no sooner were KR’s hopes of a genuine fightback raised than they were dashed as a thrilling crossfield broken-play attack by Saints ended with Richardson kicking through for Mark Percival to ground the ball in the 47th minute. There was no goal from Richardson this time.
Rovers enjoyed more possession as the half went on but they were unable to crack the Saints defence despite having a try disallowed in the closing stages.
With the game nearly up, Barba went almost the length of the field as he outsprinted the demoralised chasing cover to score his second of the night.
St Helens: Barba, Makinson, Morgan, Percival, Grace, Fages, Richardson, Amor, Roby, Thompson, Peyroux, Taia, McCarthy-Scarsbrook. Substitutes: Smith, Douglas, Knowles, Lees.
Hull K R: Quinlan, Shaw, Salter, Vaivai, Wallis, Marsh, Blair, Johnson, Cator, Greenwood, Clarkson, Tickle, Donaldson. Substitutes: Scruton, Masoe, Kavanagh, Atkin.
Referee: Gareth Hewer (RFL)