Lansdowne and Terenure College have secured home advantage in the Ulster Bank League play-offs following an eventful day in Division 1A.

Leinster 'A' scrum half Adam Griggs, who was sprung from the bench, was Lansdowne's hero as his 79th minute try earned a 27-20 bonus point win at the expense of Cork Constitution.

The disappointment of the defeat lifted slightly for Cork Con when they learned that UCD and Ballynahinch had both lost, meaning that the Leesiders’ losing bonus point was enough to move them back into the top four.

The afternoon had begun brightly for Cork Con as Munster prospect Darren Sweetnam touched down for the second week running. Lansdowne's patience was tested until Conor McKeon's neat offload played in hooker Tyrone Moran for an unconverted try in the right corner.

An opportunist try by Crok Con outhalf Tomas Quinlan restored his side’s five-point advantage, but a late surge from Lansdowne made it 12-10 at the break as Tom Daly’s purposeful break was finished off by his centre partner Tom Farrell and McKeon converted.

McKeon and Quinlan swapped penalties early on the resumption before Lansdowne, playing with increased confidence, swept through for their third try - a memorable run on the right wing saw Farrell break free to complete his brace in the 53rd minute.

McKeon missed the conversion, though, and with 13 minutes remaining a Lansdowne handling error allowed the speedy Sweetnam to latch on to the loose ball and race in under the posts. Quinlan’s levelling conversion set up a grandstand finish.

However, Lansdowne produced the goods when it mattered most as Griggs ghosted through a minute from the end to score the game’s decisive try and give the headquarters club their 13th win in 16 league outings.

Centre Stephen O'Neill had a day to remember, scoring three of Terenure College's six tries as they won their Dublin 6W derby with St. Mary's College on a 41-24 scoreline.

A James Thornton pass put O’Neill over for a timely try on the stroke of half-time, and he added two more in the second half. Mary’s, who remain relegation trouble, made Terenure sweat with a penalty try that closed the gap to 34-24, but a Niall Lalor turnover led to Shane Donovan’s clinching seven-pointer.

Young Munster boosted their hopes of avoiding the drop with a vital 20-17 victory over UCD at the Belfield Bowl. The Cookie's completed a season's double over the students, adding to last week's defeat of bottom side Dolphin.

John Staunton's charges hung in there after leaking early tries to prop Liam Hyland and winger Adam Byrne, with the latter profiting from Stephen Murphy's outside break and offload. Willie Staunton kicked his second penalty and a penalty try cancelled out a Liam Bourke effort as Munsters cut the deficit to 17-13 by half-time.

UCD had two forwards in the sin-bin during the first half, including recent Leinster debutant Ross Molony, and that helped to swing the game in the visitors’ favour. The power of the Young Munster pack saw them muscle their way to a victory which should have been more comfortable.

Munsters dominated an early scrum and a penalty led to a threatening maul in the 22. With an overlap out wide, a long pass gave fullback Shane O’Leary the simplest of finishes. Staunton converted from the touchline for good measure, making it 20-17.

Young Munster messed up a two-on-one overlap then as scrum half Rob Guerin, who had winger Diarmaid McCarthy outside him, tried to break through the final tackle and knocked the ball on.

UCD had plenty of late pressure too, camping close to the Munsters’ line with the visitors down to 14 men. However, two knock-ons allowed the Cookies to clear and after turning down a shot at goal, a final knock-on blew the students’ chances of victory.

The Scannell brothers, Rory and Niall, were the toast of Dolphin as they combined for 19 points in the Cork club's impressive 24-22 defeat of defending champions Clontarf at Castle Avenue.

It was a hugely important result for the division’s bottom side who still have a mathematical chance of avoiding relegation - they are seven points worse off than St. Mary’s (ninth) and nine behind Old Belvedere (eighth) with two rounds remaining.

Tries from Welsh lock Chris Rowe and the Scannell brothers had Dolphin leading 21-15 at half-time. Clontarf number eigh Tony Ryan’s try from a break from outside the 22 put his side back in front but outhalf Rory Scannell had the final say for Dolphin, brilliantly converting a penalty from wide out on the left to complete his 14-point tally.

The reversal means Clontarf still have a job to do in terms of confirming their presence in the play-offs. Andy Wood’s men remain third overall on 42 points, with Cork Con (37), Ballynahinch (36) and UCD (36) leading a group of clubs who are still in the hunt for a semi-final spot.

At Anglesea Road, Old Belvedere finally put a bad run of results behind them with a morale-boosting 40-14 triumph over play-off chasing Ballynahinch. The five tries-to-two success moved Old Belvedere up to eighth and out of the relegation/promotion play-off position.

Number eight and captain Jonathan Slattery led by example with a two-try haul, while lock Conor Owende and backs Peter Robb and Charlie Rock also touched down. Josh Glynn kicked the winners’ other 15 points.

DIVISION 1A RESULTS:

CLONTARF 22 DOLPHIN 24, Castle Avenue

Scorers: Clontarf: Tries: Sam Cronin, Matt D'Arcy, Anthony Ryan; Cons: David Joyce 2; Pen: David Joyce

Dolphin: Tries: Chris Rowe, Rory Scannell, Niall Scannell; Cons: Rory Scannell 3; Pen: Rory Scannell

HT: Clontarf 15 Dolphin 21

LANSDOWNE 27 CORK CONSTITUTION 20, Aviva Stadium back pitch

Scorers: Lansdowne: Tries: Tyrone Moran, Tom Farrell 2, Adam Griggs; Cons: Conor McKeon 2; Pen: Conor McKeon Cork Constitution: Tries: Darren Sweetnam 2, Tomas Quinlan; Con: Tomas Quinlan; Pen: Tomas Quinlan

HT: Lansdowne 12 Cork Constitution 10

OLD BELVEDERE 40 BALLYNAHINCH 14, Anglesea Road

Scorers: Old Belvedere: Tries: Conor Owende, Jonathan Slattery 2, Peter Robb, Charlie Rock; Cons: Josh Glynn 3; Pens: Josh Glynn 3

Ballynahinch: Tries: Rodger McBurney 2; Cons: Adam Craig 2

HT: Old Belvedere 18 Ballynahinch 7

UCD 17 YOUNG MUNSTER 20, Belfield

Scorers: UCD: Tries: Adam Byrne, Liam Hyland, Liam Bourke; Con: Liam Bourke Young Munster: Tries: Shane O’Leary, Penalty try; Cons: Willie Staunton 2; Pens: Willie Staunton 2

HT: UCD 17 Young Munster 13

TERENURE COLLEGE 41 ST. MARY’S COLLEGE 24, Lakelands Park

Scorers: Terenure College: Tries: Robbie Smyth, Harry Moore, Stephen O’Neill 3, Shane Donovan; Cons: James Thornton 3, Mark O’Neill; Pen: James Thornton St. Mary’s College: Tries: Marcus O’Driscoll, Penalty try; Con: Ray Crotty; Pens: Ray Crotty 4

HT: Terenure College 20 St. Mary’s College 17