. Up north, Colm Atkinson scored two tries while AJ Derwin converted one of those scores, kicked three penalties and a drop-goal to keep Harlequins in the hunt for a place in the play-offs.
Lansdowne moved into second place thanks to their 40-3 win over Dungannon in Stevenson Park while a late try from Paddy O'Sullivan helped Buccaneers to a 20-10 win over Shannon at Ericsson Park, a result that effectively ends the title holders interest in the latter stages.
Galwegians kept their hopes of the play-offs alive with a remarkable come-back in Stradbrook where they came from being 31-12 down at half-time to end up 33-31 winners.
The fight to avoid relegation, between Co Carlow and UL Bohemians looks like it will go right down to the last day. Carlow beat UCD 31-8 in Oak Park and Bohs edged out St Mary's 23-17 in a tense Thomond Park encounter.
Results - Division One. Belfast Harlequins 24-15 Clontarf.Blackrock College 31-33 Galwegians.Buccaneers 20-10 Shannon.Co Carlow 31-8 UCD.