Replacements: Alan Trenier, Adam Howard, Killian O'Neill, Fergal Lawlor, Peter Robb.
Replacements: Will Foley, Darren O'Shea, Dave O'Mahony, Sean McKeown, Damien Attridge.
Clontarf's back-to-back losses to UCD and Lansdowne has opened the door for 'Belvo to reclaim the title they last secured in 2011.
With 23 points separating them and Dolphin in the Division 1A table before kick-off, they were favourites to return to the summit.
Yet, Dolphin also had good reason to produce their best form in the capital as they needed one more win to be certain of their Division 1A status.
With that in mind, it came as little surprise that the visitors made such an impressive start to proceedings.
Their young out-half Rory Scannell missed an awkward penalty opportunity on the left wing just two minutes in but Dolphin broke the deadlock three minutes later.
The move for the opening try was instigated by a strong drive on the right and hooker Niall Scannell, who lined out alongside his brother Rory in the Munster 'A' team's recent British & Irish Cup loss to Leinster 'A', powered over impressively in spite of the best efforts of the 'Belvo defence.
Rory Scannell converted and Old Belvedere's initial reaction to the concession of seven points was positive,.
Full-back Glynn, who moved from his customary role on the wing in the absence of captain Daniel Riordan, had an excellent opportunity to open his side's account on ten minutes.
His kick into a tricky breeze drifted well short of the mark however, and when referee Peter Fitzgibbon awarded a 35-metre penalty to Dolphin 14 minutes in, Rory Scannell split the posts emphatically.
Because of the significance of the game, there was a certain degree of nervousness about the 'Belvo play, but a successful three-pointer from close range by Glynn did help to ease the pressure on Paul Cunningham's men.
Indeed, as the minutes passed by, 'Belvo were making more of an impact inside the Dolphin half and the dependable Glynn was on hand to register a second successful penalty just shy of the half hour mark.
Slowly but surely, the hosts were starting to dominate the possession stakes and creating a number of phases close to the Dolphin line.
They could not quite break down the stern defensive resistance offered by the Munster side, but a third routine score from the kicking tee by Glynn cut the deficit to the bare minimum - 10-9 - in time for the interval.
'Belvo were starting to settle into their more accustomed rhythm and just four minutes after the restart, they hit the front for the very first time.
Further indiscipline by Dolphin once again presented Glynn with a kick in front of the posts and although 'Belvo winger Aidan Wynne found himself in the sin-bin six minutes into the half, he was joined by Dolphin lock Chris Rowe whose infringement had led to Glynn's fourth penalty of the day.
During the absence of this aforementioned duo, Glynn had his toughest kick of thegame from just inside the opposition half, but he displayed nerves of steel to move 'Belvo into the driving seat.
Either side of this brace by Glynn, Rory Scannell passed up a chance to restore the Dolphin lead, but just when it seemed like the home side were holding all the aces, Steve Ford's side once more threatened to upset the odds.
A terrific move across the 'Belvo line found its way to centre Cian Bohane and he put winger O'Shaughnessy through in the right corner. Rory Scannell missed the conversion, leaving the sides on level terms as the final quarter approached.
A massive effort was still required if 'Belvo were going to get over the finish line but thanks to powerful surges by Leinster star Leo Auva'a, Steve Crosbie and former Blues out-half Shaun Berne, they had Dolphin on the back foot for most of the closing stages.
For all their strong work in attack though, it was left to the outstanding Glynn to seal the points for Old Belvedere.
His pinpoint place-kicks in the 61st and 76th minutes, with Dolphin losing centre John Gleeson to the sin-bin, helped to set up a potential title-winning game away to Garryowen next Saturday.
Referee: Peter Fitzgibbon (IRFU)