The Myreside men knew that they just had to reach the quarter-finals at Riverside Park to get the points they needed to get them over the line after 10 tournaments.
And they made the last eight comfortably, defeating Gala 35-5 before getting refocused on the job in hand.
In the next round they defeated charity side Hearts & Balls before a real classic clash with the hosts in the last four.
Both sides scored three tries – Ali Harris, Andrew Skeen and Chris Scott for Watsonians – with the final conversion by Harris the deciding factor.
In the final against Melrose, the side who pushed them all the way to the overall title, Watsonians just ran out of steam.
Willie Thomson grabbed a try for the Capital men as Melrose won the event.