The visitors put in an amazing effort, especially in defence, at the Kingspan Stadium and led 14-8 with the clock heading into the red.
However, Ireland centre Enya Breen bagged a try – and converted it herself – in the 84th minute to break Scotland’s hearts.
It means Bryan Easson’s charges lost five out of five in the tournament and ended up with the wooden spoon.
Before kick-off, a minute of silence was held to mark the passing of Clare Hoppe, a member of the first ever Ireland Women's team, who was the auntie of Scotland vice-captain Helen Nelson.
Scotland got off to a confident start and took the lead after just four minutes when No.8 Evie Gallagher went over for an unconverted try from short range.
Ireland got themselves on the board in the 16th minute when No.8 Hannah O’Connor kicked a penalty.
In the 28th minute Ireland won a scrum penalty, but O’Connor missed the resultant kick and it remained 5-3 to Scotland as the half hour mark approached.
Just before the interval Ireland took the lead after a well-worked forward drive gained momentum and saw hooker Neve Jones score a try. Breen missed the conversion and it was 8-5 heading into the interval.
Scotland started the second period with good intent and they were rewarded when Nelson kicked a penalty to make things 8-8 after 52 minutes.
And just before the hour mark another Nelson penalty made it 11-8 to the Scots.
Things got even better with 18 minutes to go when a third Nelson penalty of the half made it 14-8.
Ireland were then knocking on the door trying to score into the last 10 minutes, Scotland second-row Sarah Bonar winning a crucial penalty and then replacement Emma Orr pouncing on a loose ball on her own try line to keep them out.
Ireland just kept on coming though and got their rewards through Breen.