The Red Devils ended the Tigers' unbeaten start to 2017 following a brace of tries from Ben Murdoch-Masila for the home side, with Gareth O'Brien's drop goal ultimately making the difference at the AJ Bell.
Sunday's result solidifies their place in the top eight of the standings and they will be looking to make things simpler for themselves in 2017, having only preserved their top-flight status by battling through the Qualifiers in the last couple of years.
Following a tumultuous few seasons, they seem to have a better mix this time around and Watson says Sunday's win shows they can match the best in the competition.
He said: "We've been really good in parts and just not seeing games off, so that's just set a standard that we can compete with the best teams.
"Cas are not dissimilar to how we play, so it's satisfying to get it right."
Elsewhere and in Sunday's other game in Super League, Wigan went above Cas in the standings, despite only managing to draw 16-16 at home to Huddersfield.