Blackrock opened at Stradbrook in a blaze and scorched Clontarf with two early tries. The northside team came back, landed a couple of penalties, then hit Blackrock with two tries of their own in the closing four minutes of the first period to trail 20-18. The first half in itself was a half of two halves. To the home-side's joy so was the second.
Blackrock, with lock Bob Casey and prop Paul Wallace warming the bench, sensed the urgency of a swinging game with little pattern and both entered the match soon after the restart. At that stage neither team could honestly declare they held a dominant position. A penalty from James Dempsey, his third, gave Clontarf the lead briefly at 20-21 until Farrell, who kicked three penalties and three conversions, re-established the home advantage for 23-21.
Playing with the wind, Clontarf, with the more aggressive pack and the wind behind, frustrated their opponents in the second half, fullback Kevin Nowlan launching down 50 and 60-yard kicks and forcing Blackrock to make the hard yards back towards their clubhouse.
But there was little penetration in Clontarf's offensive moves, the ball rarely arriving out quickly enough to wrong-foot the committed defence. The earlier holes that had allowed Padraig Lynn and Ronan O'Reilly collect tries in the first half had closed.
Along with second row John Fitzgerald, who was magisterial in the home-side lineouts, Wallace, and the two replacements, Gavin McCarthy and Casey, steadied their team in an area that Clontarf had initially dominated through Donal Sheehan and Ben Gissing.
In the latter stages Blackrock then set about the visitors, particularly over the final 10 minutes.
With the scoreline at 23-21 on 73 minutes, Gary Browne benefited from good yardage from Casey on the left for his side's third try before substitute scrumhalf Ben Willis added the fourth four minutes later after O'Neil had run and kicked the ball 50 yards.
The win secure, Blackrock rejoiced after a performance that was both encouraging and wobbly.
Scoring sequence: 6 mins, J Dempsey pen 0-3; 11 mins, A Grealey try, E Farrell con 7-3; 14 mins, D Popplewell try, Farrell con 14-3; 19 mins Farrell pen 17-3; 22 mins Farrell pen 20-3; 30 mins J Dempsey pen 20-6; 36 mins R O'Reilly try, Dempsey con 20-13; 40 mins P Lynn try 20-18; 42 mins J Dempsey pen 20-21; 47 mins Farrell pen 23-21; 73 mins G Browne try 28-21; 76 mins B Willis try, Farrell con 35-21.
Blackrock: J Corry; A O'Neil, N Turner, A Grealey, G Browne; E Farell, D Popplewell; I McLaughlin, G McEvoy, N Treston, S Fallon, J Fitzgerald, D McGettigan, R Woods, M Carroll. Subs: B Casey for Fallon 43 mins. G McCarthy for McGettigan 48 mins. P Wallace for Treston 51 mins. B Willis for Popplewell 59 mins.
Clontarf: K Nowlan; T Tiernan, A Reddan, J Downey, O Winchester; J Dempsey, R O'Reilly; W O'Kelly, M Kennedy, A Clarke, D Sheehan, B Gissing, D Quinn, P Lynn, D Moore. Subs: T Kearns for O'Kelly 51 mins. A Dignam for D Quinn 60 mins.
Referee: D Keane.