Replacements: Jason Cronin, Mike Essex, Mike Cullane, Brian Smith, David Evans.
Replacements: Mark Cooney, Adam Howard, Michael Oyuga, Kevin Barden, Gearoid McDonald.
They welcomed back fit-again Munster flanker Niall Ronan who scored a late try to deny a spirited Old Belvedere even a losing bonus point.
It was a tough finish for the Dublin 4 club who got no reward for battling back to make it 17-all.
They might have increased the mounting Shannon troubles but goal-kicking winger Josh Glynn was wide with a penalty effort. After that let-off Shannon turned on the style in an amazing final six minutes.
Out-half and captain Tadhg Bennett dropped a goal to restore Shannon's lead and then his half-back partner Rob Guerin landed a penalty.
Ronan's touchdown from a close-in ruck was the final score of an exciting duel which leaves bottom side Shannon just four points behind eighth-placed 'Belvo.
Guerin popped over a penalty to put Shannon in front after eight minutes and he was inches wide with another effort.
A prop from each side was sin-binned during which period Shannon had their first try when Connacht-capped full-back James Loxton finished off a fine attacking move - well-placed passes from Richie Mullane and Ronan put him over in the right corner.
Bennett converted to make it 10-0 and when a second Belvedere forward was binned the visitors had only 13 players on duty for a brief few minutes.
During that time, Shannon's robust inside centre Mullane raced over and Bennett's conversion made it 17-0. Mullane cut a great line inside the 'Belvo 22, running hard onto David O'Donovan's deftly delayed pass to score to the left of the posts.
If Shannon thought they were in for a stroll around Thomond Park in the second half, Old Belvedere had other ideas.
Their number 8 and captain Jonathan Slattery and lock Josh Eden-Whaitiri both notched tries which Glynn converted. Slattery galloped over from a close-in ruck to give his side a timely boost, and then came the try of the match.
Eden-Whaitiri weaved his way past two Shannon players just outside the visitors' 22 and then charged clear over the halfway line.
Mullane and Loxton closed him down, but the big New Zealander found support and kept running for the return pass which put him over in the right corner for a tremendous breakaway score.
Glynn also kicked a penalty and suddenly it was all-square and Andy Dunne's men were right back in contention.
But Shannon have always been known for their spirit and they finished powerfully for a precious victory which keeps their heads above water in a fascinating relegation battle.
Referee: Mark Patton (IRFU)