Munster-contracted Scannell was the stand out performer in an excellent Dolphin display once they found their feet in the latter stages of a first half during which they were generally outplayed.
Buccaneers stormed into a 15-0 lead inside 28 minutes but paid a heavy price when scrum half Graham Lynch was sin binned shortly before the interval.
Dolphin clawed back 10 points before the break, equalised immediately afterwards and then matched the visitors blow for blow before striking late through Scannell.
Having failed narrowly to Old Wesley in their last home game, this time the late rally was rewarded to the delight of coach Feargus O’Donoghue.
“We felt we deserved to come away with the points against Wesley based on our second half performance but we had to be happy with a losing bonus point; in this one we were a bit fortunate, but then again you have to make your own luck sometimes.
“We try to work on the positives all the time and we have put up two consecutive wins since that game against Wesley. It’s our third win of the season and the lads are certainly getting better although how we will be next week in terms of injuries, I have no idea.
“The good thing is that the team has finished all of our last four games attacking and if you can do that then it’s not a bad sign. If you get the result on top of it then that is great.”
However, he admitted his side cannot afford to have slow starts like Saturday.
“I don’t know why, but we were very flat, they really went at us and we had to make the few changes to liven it up.
“I can’t put a finger on it because our preparation was no different to the last few matches.”
Dolphin hardly had time to organise themselves when they had conceded two tries. Each of them, from wingers Rory O’Connor and Eoin O’Reilly, was the result of speed of thought and sleight of hand.
Out half Conor McKeon converted one and then kicked a penalty to help his side into that hefty lead. But Scannell showed his own ability to break the Buccaneers’ defence with a storming run. The move broke down but, as Dolphin scrambled to recycle possession from a ruck close in, Lynch disrupted supply and was shown yellow.
Scannell kicked the penalty and within three minutes he converted a superb try from full back Shane McAuliffe.
Cian Bohane got the second on the resumption to make it 15-15.
Scannell kicked two penalties either side of one from McKeon and then stayed calm to strike for the winner after Callum Boland had scored a third for Buccs to give his side a 23-21 advantage entering the last few minutes.
S McAuliffe, W Hanly, R O’Sullivan, C Bohane, R Reardon, C McGovern, D Foley, J Leahy, D Byrne, K O’Halloran, C Rowe (captain), D O’Mahony, R O’Herlihy, B Fitzgerald, J Fitzgerald.
A Mason, R O’Reilly, R Scannell, K O’Leary, K O’Keeffe.
C Boland, R O’Connor, A Gaughan, B Carty, E O’Reilly, C McKeon, G Lynch, J Walsh, S Flanagan, M Staunton (captain), M Mannion, D Qualter, R Farrell, R Moloney, S McVeigh.
G Halligan, S Meunargia, C Ronayne, A Hayman, B Corcoran.
M Connolly (IRFU)