Neither side threatened in the opening 20 minutes of the game, but a break from Lewis Tierney helped set Kirk Dixon up for the opening try for Castleford, before Grant Millington doubled their lead just before half time.
James Clare added a third early in the second half, but Josh Charnley managed to get Wigan off the mark with the home side's only try of the match.
Tries from Travis Burns and Alex Brown helped the visitors take the lead, while Burns had a second ruled out for a knock on.
Greg Eden managed to add a third for Hull KR before half time, while Burns and Saints' Paul Wellens were sent to the sin bin for fighting.
Francis Meli got the hosts back into the game with a try early in the second half, but a series of penalty kicks from Michael Dobson helped the Robins to keep adding to their score throughout the second 40 minutes.
Results in full: St Helens 12-24 Hull Kingston Rovers, Wigan Warriors 4-18 Castleford Tigers, Huddersfield Giants 60-16 Catalans Dragons