Bohs secured the Division Two top spot on a final afternoon which saw idle Dolphin slip from first to fourth in the promotion hunt.
The Limerick men did it the hard way though, overcoming a fifth-minute try from Ballynahinch scrum-half Paul Marshall to win 22-5 up north.
Metronome-like penalties on 12, 15, 20 and 40 minutes from fly-half Ben Martin helped the students to a 12-5 half-time lead.
While 'Hinch lost lock Gareth Rourke to a yellow card early in the second half, Bohs ploughed ahead, although Johnny Cullen's 63rd-minute try was ruled out for a forward pass.
12 minutes later, Martin's fifth penalty, added to the fly-half's touchline conversion of an Ian Hanley try made certain of the points for the visitors.
Mary's must have been thankful for man-of-the-match fly-half Barry Lynn at Templeville Road on Saturday, as he contributed a stunning 28 points to their 33-19 win over relegation-promotion play-off bound Barnhall.
Lynn chipped in with a try, a conversion, six penalties and a drop goal as the Dubliners also secured a home semi-final date against third-placed UCC.
Former Ireland Under-21 Richard Lane scored two tries for UCC at the Mardyke as they accounted for Thomond 47-18 and booked their place in next Saturday's Division One relegation-promotion play-off with Lansdowne.
Elsewhere, Malone chalked up their sixth win of the campaign as they edged strugglers Highfield 26-24.
Although Highfield went 12-0 up initially in front of a vocal Woodleigh Park attendance, the Ulster visitors took a healty lead through tries from Rhys Botha before the break, and further efforts from Simon Bailey, John Amos and substitute Simon Cahill.
Highfield fly-half Conor Quaid then summoned up a bonus point-securing try for the Cork men on 70 minutes - ensuring their Division Two survival.
His conversion attempt for a draw was blocked.
2004/05 Season Ups And Downs:
AIB LEAGUE: Saturday, April 16 Results:
Ballynahinch 5 UL Bohemians 22, Ballymacarn ParkDe La Salle Palmerston 24 Bective Rangers 18, KilternanHighfield 24 Malone 26, Woodleigh ParkOld Crescent 26 Midleton 31, RosbrienSt Mary's College 33 Barnhall 19, Templeville RoadUCC 47 Thomond 18, The MardykeWaterpark 18 Old Belvedere 13, BallinakillYoung Munster 48 Terenure College 29, Tom Clifford Park