Replacements: Adam Howard, David Gilchrist, Colin Mallon, Ben Woods., Kevin Barden.
Replacements: Alex Simpson, Ed Rossiter, Conor Kindregan, Brian Walsh, Alan Rossiter.
But a try right at the death from flanker Ian Condell, which full-back Ben Martin converted, saw Bohs bring their four-game losing streak to an end.
Andy Dunne's 'Belvo outfit were eager to bounce back from a demoralising 40-3 defeat away to Young Munster last time out.
Both of these clubs have endured spells of inconsistency since the start of the season, with UL Bohs travelling to Dublin keen to halt a slide which has left them second-from-bottom in the table.
Old Belvedere eeked out a 16-10 half-time lead after a fast-paced opening 40 minutes that was full of strong running but a smattering of costly handling errors.
It was nip and tuck throughout as UL director of rugby Mossy Lawler, playing at outside centre, followed up on good work by Niall Kenneally for a try. He was responding to an earlier unconverted effort from Glynn.
Martin converted and also kicked a penalty but two penalties from Glynn and a 38th minute try from left winger Eddie Devitt ensured the hosts were ahead at the turnaround.
'Belvo had to cope with the 32nd minute sin-binning of prop Pat O'Regan and after he returned, the elusive Devitt nipped in for his second five-pointer on the hour mark.
Back came Bohs, showing tremendous battling qualities as Martin converted a penalty and then brilliantly added the extras to young winger David Johnson's 69th-minute try. That set up a nervy finale with 'Belvo now just 21-20 in front.
Ultimately they were unable to hold on as although Glynn took his personal haul to 14 points, Colm Tucker's side managed to salvage the win from the jaws of defeat as Condell drove over in injury-time.
Referee: David Wilkinson (IRFU)