Replacements: Shane Delahunt, Ian Prendiville, Rhodri Jones, Ian Burke, Tom Farrell.
Replacements: Cathal O'Flynn, Tom Byrne, David Hegarty, Peter du Toit, Timmy McCoy.
It was perhaps apt that it was Lansdowne who delivered a dent to Clontarf's title hopes as they had defeated the north Dubliners to secure the top flight crown last season.
Having beaten their main challengers on home soil recently, 'Tarf seemed to be odds-on to claim a first ever league title, but following their loss to UCD at Belfield a victory was badly needed at the home of Irish rugby.
In contrast, three defeats on the trot - including two at home - had seen Mike Ruddock's Lansdowne side lose third place to UCD and if they were to halt this losing sequence, a positive start was required against Clontarf.
The return of former Cork Constitution star Scott Deasy to the starting line-up was certainly a boost and just three minutes in, he comfortably slotted a 35-metre penalty between the posts.
Having struggled to find their feet in the first quarter against the students last Saturday, 'Tarf chased a quick response to Deasy's opener.
After his eighth minute penalty was confidently converted, the reliable David Joyce kicked the visitors into a 6-3 lead via a close range effort on 14 minutes.
However, given their recent history with the Castle Avenue outfit, Lansdowne were never going to be pushovers and by the end of the first quarter, they restored their advantage with the first try of the night.
There did not appear to be much danger initially, but when Ireland Under-20 prop Peter Dooley received the ball not far out he powered through in clinical fashion.
A simple Deasy conversion ensured that Lansdowne's lead stood at four points and although 'Tarf continued to see plenty of the ball, strong work by the opposition defence brought a number of promising moves to an end.
Having remained watertight for much of the current campaign, 'Tarf's defence has come under immense pressure in recent weeks.
A strong 30th minute maul on the right flank was eventually finished off by tighthead Adam Boland.
Three minutes before the interval, ever-influential centre Mark Roche broke through for Lansdowne's third try following an almost identical move on the far side.
Deasy added both conversion to give the headquarters club a surprise 24-6 cushion approaching half-time and for the second game in succession, 'Tarf were staring defeat in the face.
There was some late hope for Andy Wood's charges as lock Conor O'Keeffe burrowed over for a precious score. Joyce added the extras to reduce his side's arrears to 24-13.
The sin-binning of Lansdowne number 8 Brian Moylett - issued by the soon-to-be retired Alain Rolland, in his final game at the Lansdowne Road venue - was another potential boost for 'Tarf after the restart, and having an extra man in the wide open spaces of the Aviva Stadium certainly had its advantages.
Yet, the current league leaders were facing a Lansdowne side that was displaying all the grit and determination that made them champions just twelve months ago.
Much of the play in the third quarter was confined to midfield which certainly played into the hands of the Dublin 4 club.
Nevertheless, their perseverance finally paid off for 'Tarf 13 minutes from the end as lightning left winger Max McFarland cut through underneath the posts. The conversion was expertly slotted home by Joyce to reduce the gap to just four points.
Unfortunately for Clontarf, this turned out to be a false dawn and just moments after McFarland's effort, Lansdowne registered the defining try of the game.
A beautifully weighted kick from Deasy enabled Foster Horan to go over under the posts. With key man Deasy adding five points to his personal tally - the conversion was followed by a late penalty - the result was effectively decided.
Clontarf's Killian Lett managed to break through the Lansdowne cover one minute from time, but his converted effort was the last score that the visitors could muster.
The outcome at the Aviva Stadium means that all eyes will be on Old Belvedere's penultimate round clash with Dolphin now to see if they can take advantage of this slip-up.
Referee: Alain Rolland (IRFU)