Stephen Murphy, Daniel Leavy and Alex Kelly scored tries to help the students on their way, while Garryowen could only manage a single try from Harry McNulty.
Clontarf’s win over Dolphin puts them in third and Young Munster are in fourth despite losing to champions Lansdowne at the Aviva Stadium.
Lansdowne scored four tries for a bonus-point win but Young Munster, at least, got a losing bonus point thanks mainly to the scoring effort of Brian Haugh with a try, conversion and five penalties.
Gavin Dunne was equally accurate with the boot for St Mary’s College and his five penalties helped his side secure a 15-9 win over Ballynahinch.
In Division 1B, Terenure’s narrow away victory over Belfast Harlequins keeps them top, but only on points difference from Buccaneers, who also won on the road.
Corinthians take third place following a more impressive 27-5 win at Blackrock and UL Bohemians struck another blow for the away teams when they beat Malone 31-6.
The single home win of the weekend in the section was at Coonagh, where Shannon beat Dungannon 17-6 with the help of Munster men Duncan Casey and Luke O’Dea.
Ulster clubs have enjoyed a fruitful start to the Division 2A campaign. Ballymena, City of Derry, Queens University and Rainey Old Boys fill the top four places. At the other end, Highfield and Bruff are in trouble.
Sundays Well are in a similarly difficult predicament in Division 2B without a win or even a point after three games.
This week they lost to Nenagh Ormond and the 20-7 win for the Tipperary side puts them in pole position, a point ahead of Armagh, who had a decisive 32-9 win over newcomers Tullamore.