Both sides needed a win at all costs to save their season but with the sides level at 10-10 at the interval Buccs stole the show in the second-half.
Champions Shannon were completely dominant in possession but couldn't make it count on the scoreboard.
Buccs soaked up the pressure and attacked with precision and Paddy O'Sullivan dived over on 75 minutes to seal the win, out-half Lee Turner converting to bring his tally to 10 for the day.
Final Score: Buccaneers 20 Shannon 10
Meanwhile at Dooradoyle Garryowen put a serious dent in Ballymena's AIL ambitions with a deserved 11-6 victory.
Garryowen led 11-6 at the break thanks to two penalties from Killian Keane and a try from John O'Sullivan.
Ballymena's first half scores came from two penaties from out-half Rob Smart. Garryowen took complete control after the break with two tries from Paul Neville and a third from Kevin O'Riordain.
Ballymena did manage tries from Ruben Aiono and Jason Taggart.
Final Score: Garryowen 36 Ballymena 16
Other Division 1 Results
Belfast Harlequins 24-15 Clontarf. Blackrock College 31-33 Galwegians. Co Carlow 31-8 UCD. Dungannon 3-40 Lansdowne. Terenure College 17-25 Cork Constitution. UL Bohemians 23-17 St Mary's College