Bedrock inflicted a surprise defeat on the returning Samcro in the WKD Hurdle at Down Royal.
The Gordon Elliott-trained Samcro carried all before him in the novice division last season, winning his first four starts including the Ballymore Novices' Hurdle at the Cheltenham Festival.
He fell on his final outing of the campaign in the Punchestown Champion Hurdle and after much deliberation during the summer months, it was confirmed on Monday he would remain over the smaller obstacle this term - rather than pursue a career over fences - with a view to having a tilt at the Champion Hurdle at Cheltenham in March.
The Gigginstown House Stud-owned six-year-old was a prohibitively-priced 4-9 favourite for his comeback under Jack Kennedy and all appeared to be going according to plan for much of the two-mile contest.
Samcro got a lead from Galway Hurdle winner Sharjah and Ruby Walsh before moving to the front rounding the home turn, but he did not quicken as anticipated on the run to the final flight and was soon claimed by Iain Jardine's Scottish raider Bedrock.
Elliott admitted to being disappointed by Samcro's defeat - but hopes he will put up a much-improved performance in the Morgiana Hurdle at Punchestown on November 18.
Elliott said: "You are always disappointed when you don't win. It's the start of the season and he travelled and looked like he was going to win and he just got a bit tired going to the second-last. He picked up and galloped then to the line.
"If you go through ratings he probably ran about 3lb or 4lb below his best. It's disappointing he didn't win but we have to look at the positives - he jumped and he's home in one piece.
"I know there is more in the horse than today. He gave the winner a good bit of weight. Both the winner and the third horse are race-fit. It's our first run since we fell at Punchestown and we haven't been on grass this year.
"What is it they say - 'we might not have won the battle, but we'll win the war'. I haven't lost faith in the horse.
"He'll go for the Morgiana in Punchestown and with a bit softer ground and faster gallop we might see a different horse."
The 12-1 shot Bedrock, who won a Grade Three at Tipperary last month, picked up well on the run-in and was ultimately well on top at the finish in the hands of Rachael Blackmore.
Jardine revealed Bedrock is set to move on to pastures new after being bought by American-based owners earlier this month, but he hopes to persuade them to keep him in Britain for a little longer at least.
He said: "I'm delighted with him and I just think our horse is really improving. We were fourth in the Galway Hurdle and the the Galway Hurdle winner is five lengths back in third today, so we're turned that form around.
"He won easily at Tipperary last time and didn't really have a race that day. He's had a race today, but he's up against the best of the best.
"He's been sold to race in America, but I hope he'll stay here for the time being.
"I'll have to speak to the new owners, but it would be good to keep him and aim for something like the Fighting Fifth at Newcastle and if that went well you'd have to look at the Champion Hurdle.
"We'll see what happens. It's a great result today, anyway."