Triple Gold Cup-winning rider Jim Culloty enjoyed Festival success as a trainer when Lord Windermere took the RSA Chase at Cheltenham.
He possibly looked a fortunate winner, however, as the Willie Mullins-trained Boston Bob crashed out at the final fence when going well in front.
That left Lord Windermere (8-1), ridden by Davy Russell, to get the better of Lyreen Legend by a length and three-quarters and give Culloty, who will be forever associated with the great Best Mate, a first winner at the meeting since he gave up riding.
Hadrian's Approach was six lengths away third.
A steady pace was set by Theatrical Star, with Goulanes and Houblon Des Obeaux close up.
But the favourite Unioniste was never able to make a serious challenge when the race hotted up coming down the hill.
Boston Bob took it up after the third-last under a decisive move by Paul Townend.
He quickly went a few lengths clear only to fall at the final fence to give Ireland a fifth success at the Festival.
Russell said afterwards: "I've only ridden him once at home, so all the credit goes to Jim Culloty, who has instilled confidence in him.
"Jim's done a marvellous job. "I only steered him today and he was in super order."
Culloty added: "We knew this horse would like Cheltenham and it's all paid off.
"I fancied him like mad - I thought he'd love the ground here.
"I told Davy to ride him to get the trip. They went no pace and it suited us.
"He's the best horse I have and it was all about getting him here.
"Tom Doyle deserves a lot of the credit, he's taught him well and the first time he rode him he said to me 'this is the one you've been waiting for'.
"I fancied him like mad - I thought he'd love the ground here" - Culloty on Lord Windermere
"You get nervous 30 minutes before going out to ride in a Gold Cup, but I have been nervous for the last six months with this lad.
"I have 13 boxes and he is in box 11, and when I work my way down to him on a morning I just pray that he is OK.
"I wouldn't have thought he would run again this year, we purposely hadn't run him over three miles on heavy ground but he will have had a hard enough race today.
"As for next year we haven't even thought about it, this has been the long-term plan.
"We didn't bring him here last year thinking about today."
When asked if Lord Windermere was a possible Gold Cup contender next season, owner Dr Ronan Lambe said: "You'd hope so.
"He's a beautiful jumper and three miles is his distance."
Trainer Dessie Hughes said of runner-up Lyreen Legend: "I was very pleased. He was beaten by a better horse on the day.
"If the ground had been heavier it might have suited us more, but no complaints."
Paul Nicholls said of Unioniste, the vanquished 5-2 favourite: "He didn't jump as well as he might have done.
"He's been running on soft ground during the winter and they went a bit quick for him.
"He's a horse who will get stronger and might be a Hennessy type next year."