Almost 150 competitors lined up for the gruelling bike and run race, organised by Durty Events, around the historic estate.
But it was Downie who led all the way to break the tape, clocking an impressive 1.23.51.
The fast-finishing Kie Jackson from Ulverston Triathlon Club made up ground during the running stage but was still over five minutes adrift of the winner.
Edinburgh’s Chris Godfree finished third.
Rosemary Byde, who also hails from the capital, was first woman with a combined time of 1.41.22 Caroline Wallace claimed second place, just ahead of Elizabeth Adams of the Westerlands club.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here