The bulk of possession in the opening 15 minutes was enjoyed by Rockwell — playing on their “home” ground of Clanwilliam Park — but they were unable to turn that into scores and found themselves 13-0 down by half-time.
Castletroy full-back Conor Linehan who got the scoring underway with a penalty awarded for hands in the ruck, somewhat against the run of play.
In the 22nd minute John Fox put more daylight between the teams when he took on a Paul Butler pass, dummied his way past the tacklers and was in under the posts, giving Linehan a straightforward conversion.
With the full-back kicking another penalty just before the interval, Rockwell were under pressure to deliver as the second half started. Scrum-half Joss Lynam was nearly over the line after eight minutes following a powerful Sean McNulty break, but Castletroy held out.
They sealed the win when a long kick into Rockwell territory bounced nicely for Rhys Joyce to score.
Scorers for Castletroy: J Fox try, R Joyce try, C Linehan 2 cons, 2 pens.
C Linehan, J Fox, C Malone, P Butler, R Joyce, M McCarthy, R Cunningham, C Humphreys, R Sweeney (capt), J Tierney, J O’Neill, R Larby, P O’Kane, D Kennedy, R Murphy.
Replacements: J Deegan for J Tierney, E Fitzgerald for C Humphreys.
W Coffey, R Deeleman, O Leahy, L Casey, L Kaminski, B Riley, J Murray, K Farrell (capt.), S McNulty, D O’Connell, J Smyth, T Brophy, J Brophy, E McCarthy, J Feehan.
Replacements: D O’Dwyer for D O’Connell, L Hickey for T Brophy, C Looby for J Brophy, S Hayes for J Murray, Fionn McCann for L Kaminski, C Flavin for L Casey.
Referee: Brian Twomey (MAR).