Lansdowne and Terenure College secured home advantage in the Ulster Bank League play-offs following an eventful Saturday afternoon in Division 1A.
Leinster 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 Cork Con out-half 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 Nure 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 Cookies 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.
Young Munster dominated an early scrum and a penalty led to a threatening maul in the 22. With an overlap out wide, a long pass gave full-back 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. Tarf number eight Tony Ryan's try from a break from outside the 22 put his side back in front but out-half 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. Belvo are now 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.