Lansdowne moved off the bottom rung - to be replaced by Carlow - as full back Brian O'Mahony kicked an injury time drop goal in their 19-17 defeat of near-neighbours Blackrock at Stradbrook.
Winger Ian Hopkins scored a second half try for Andy Doyle's visitors, after a Dave Dillon effort and three penalties from the boot of Conor Kilroy had given 'Rock a 14-6 interval lead.
Andy Tallon chipped in with three penalties and a conversion to take his season's tally up to 47 points.
At Stevenson Park, Jeremy Davidson's Dungannon got a much-needed boost as they edged a disappointing Cork Con 21-14.
An early Gillan Carruthers try and nine points from the boot of Ireland Under-21 Gareth Steenson had 'Gannon 14-3 up.
However a neat try from Con's French centre Jean-Vincent Igarza - added to by three Barry Keeshan kicks - saw the sides level at the break.
With lock Tim Barker sent off for a second yellow card, 'Gannon dug dip to move up to seventh in the standings, as scrum-half David Spence arrowed through late on for the winning touch down.
Bernie Kelly's Galwegians side picked up their second win against more noted opponents in the space of three weeks, as they defeated Connacht rivals Buccaneers 20-17, in the weekend's only other top flight game.
Justin Meagher - who was playing opposite his 'Wegians centre brother, Stuart - had a chance to draw the game at the death for the Pirates, but his penalty attempt fell back off an upright.
Meagher converted both Buccs tries from Niall Smullen and Rory McCann earlier in the second half - after 'Wegians - 10-6 conquerors of Con last month - had enjoyed a 17-0 lead at half-time.
The home side scored two tries - one from John Cleary, and the other a penalty try - as fit-again Connacht squad member David Slemen kicked two conversion and two penalties - the second just minutes into the second half.
AIB League: January 8-9 Results:
Belfast Harlequins 26 County Carlow 0, Deramore ParkBlackrock College 17 Lansdowne 19, StradbrookDungannon 21 Cork Con 14, Stevenson ParkGalwegians 20 Buccaneers 17, Crowley Park
*Dublin University v Clontarf was postponed due to an unplayable pitch
*Old Crescent v Barnhall and Young Munster v Highfield were both postponed due to unplayable pitches
City of Derry 18 Sunday's Well 3, Judge's RoadClonakilty 16 Suttonians 5, Shannonvale Cross Corinthians 12 Connemara 14, Corinthian ParkInstonians 12 Greystones 24, Shaw's BridgeOld Wesley 27 Queen's University 19, Donnybrook Portadown 11 Ards 18, Chambers LaneWanderers 15 Skerries 9, Lansdowne Road
*Bruff v Ballina was postponed due an unplayable pitch