Ireland held off a relentless Scotland in a nailbiting finish at Donnybrook to open their Six Nations campaign with a vital win.
Beibhinn Parsons' 67th-minute intercept try looked to have sealed the deal for Ireland but Emma Wassell replied for Scotland with four minutes left.
Earlier scores from Cliodhna Moloney and Sene Naoupu put Ireland in control.
Lisa Thomson's late first-half try had dragged Scotland back into the game.
The opening half hour belonged totally to Ireland, who stretched into a 13-0 lead. But Scotland's physicality soon granted them a foothold in proceedings and they were the dominant force during a tense second half.
The two sides will take part in a World Cup qualification tournament later this year, and on the basis of Sunday's showing there is little, if anything, separating the two.
Moloney spearheads Ireland's fast start
Last year Ireland's only win of the tournament came in a 22-5 win over Scotland in Glasgow, and the earlier signs in Dublin on Sunday were that the result would be similarly favourable for Adam Griggs' side.
Ireland were in control until the 27th minute, when hooker Moloney was forced off the field with a head injury.
Up until that point, the forward had been the game's dominant force, setting her stall out with a brilliant turnover on halfway inside two minutes.
Eight minutes later Moloney was found in space, and the hooker threw a dummy before straightening up and surging past three defenders for the game's opening try.
It was not long before Ireland extended their lead. This time it was Naoupu, on her 36th birthday, to benefit from an overlap on the right, bursting through a gap to score following Michelle Claffey's initial break.
Moloney remained at the heart of everything, forcing another penalty just a minute before a collision with Thomson ended her day.
Scotland superb in the scrum
After a slow start had provided little to cheer about from a Scottish perspective, they gradually wrestled control from their hosts through dominance in the set-piece.
The last 10 minutes of the first half saw Scotland rip through two Irish scrums to create excellent field position.
The second effort saw them move deep into Irish territory as they probed for an opening.
Thomson picked the perfect line to scythe through Ireland's defence as Scotland reduced their deficit to six points by the interval.
The pattern continued into the second half, when Scotland set up camp in the Ireland half as the hosts struggled to find any respite from the Blue onslaught.
Parsons makes game-winning play
Scotland's dominance was such that a try appeared something of an inevitability.
Eventually they moved the ball right with an overlap on, only for Parsons to step out of the line and execute a perfectly timed intercept.
Had she missed the move by a beat, Scotland would certainly have scored. As it was, the wing picked it off and ran the length of the pitch to put Ireland into an 18-7 lead with 10 minutes remaining.
Scotland were not done though and they rampaged back down the field. This time they found a clinical finish when Wassell spotted a space to charge through, allowing hooker Lana Skeldon to convert and narrow the gap to four with four minutes remaining.
But Ireland held out to claim a dramatic but vital win.
LINE-UPS
Ireland: Delany; Doyle, Naoupu, Claffey, Parsons; Murphy, Dane; Peat, Moloney, Djougang; McDermott, Fryday; Griffin, McMahon, Caplice.
Replacements: Dabanovich O'Mahony, Feely, Lyons, Cooney, Wall, Cronin, Keohane, Sheehan.
Scotland: Rollie, Lloyd, Smith, Thomson, Gaffney, Nelson, McDonald; Bartlett, Skeldon, Forsyth, Wassell, Bonar, Malcolm, McLachlan, Konkel.
Replacements: Wright, Muzambe, Cockburn, Cattigan, McMillan, Law, Tonkin, Wallace.