RBS UNDER-21 SIX NATIONS CHAMPIONSHIP:Scotland U21 16 Ireland U21 8, Falkirk Community StadiumScorers: Scotland: Tries: Iain Kennedy, Ross Ford; Pens: David BlairIreland: Try: Mark Kettyle; Pen: Gareth Steenson
A 45th-minute red card handed down to UCD scrum-half Cillian Willis proved crucial for the Irish as they lost their 13-game unbeaten record against the hosts at this level.
In constant rain, McDermott's charges hung in for long periods, and were only 3-0 down at the break, with the Scots fluffling five penalty chances.
They missed a further two after the restart, but with Willis sent to the line by French referee Jean-Pierre Mathieu for a ruck stamp, the game was effectively the home side's for losing.
Ireland lost lock Lewis Stevenson to a yellow card shortly before half-time, and they were 8-0 in arrears as substitute Kennedy stepped inside Mark Kettyle to touch down on 43 minutes.
Irish captain Gareth Steenson then clipped over a quick penalty goal in reply, and on 50 minutes, Belfast Harlequins' flyer Kettyle - who along with centre Andrew Trimble and Dungannon number eight Stephen Ferris - agonisingly close to a barnstorming individual try - were Ireland's stand-out players - touched down in the right corner, to level at 8-apiece.
Steenson missed the conversion, and back came the Scots. Despite losing flanker Colin White to the sin-bin, the home side netted a late penalty brace from David Blair, and White was on hand to set up his fly-half Blair for the clinching try.
Ireland next take on England U21 - still without a win in the tournament, after Friday's 20-17 loss to France U21 in Northampton - at Donnybrook (kick-off 7.30pm), on Friday, February 25.
SCOTLAND U21: Brian Archibald (Stirling County); Ben Addison (Stirling County), Nic De Luca (Heriot's), Garry Law (Hawick), Steven Manning (Ayr); David Blair (Sale Sharks), Alasdhair McFarlane (GHA); Ross Ford (The Borders and The Scottish Institute of Sport), Stuart Fenwick (Ayr), Ian Nimmo (Heriot's), Stuart Walker (Newcastle Falcons), Colin White (Stirling County), Scott Forrest (Glasgow Hawks), Neil Cochrane (Watsonians) (Capt).
(15) Mark Kettyle (Belfast Harlequins)(14) Stephen Grissing (UCD)(13) Andrew Trimble (Ballymena)(12) Kieran Geraghty (London Irish)
Replacements used: Ryan Caldwell (Dungannon) for Melbourne (43), David O'Leary (UCC) for McNamee (47), Tommy Bowe (Belfast Harlequins) for Geraghty (48), Barry Keeshan (Cork Constitution) for Steenson (72). Not used: Joseph Merrigan (Corinthians), Eamonn Bracken (Buccaneers), Anthony Kavanagh (Garryowen).
HT: Scotland U21 3 Ireland U21 0; Yellow cards: Stevenson (29 mins), White (67). Red card: Willis (45). Attendance: 2,500Referee: Jean-Pierre Matheu (France)
Italy U21 3 Wales U21 40England U21 17 France U21 20