Samcro suffered a shock defeat on day one of the Down Royal Festival as Scottish raider Bedrock clinched a 12-1 victory in the WKD Hurdle.
Rachael Blackmore produced a superbly judged ride on Bedrock to move into the lead at the second last and held on to win by more than a length.
The Gordon Elliott-trained Samcro went off as 4-9 favourite after his brilliant novice campaign last season.
Samcro's four wins included victory in the Cheltenham Novices Hurdle.
The Gigginstown House Stud-owned horse fell in the Punchestown Champion Hurdle in April but was still rated as 11-4 favourite for next March's Champion Hurdle at Cheltenham going into Friday's race in Northern Ireland.
Bedrock recently bought by US-based owners
The Iain Jardine-trained winner, who earned a Grade Three success at Tipperary last month, picked up well on the run-in and was ultimately well on top at the finish in the hands of Blackmore.
With only four runners going to post, Willie Mullins' Galway Hurdle winner Sharjah was five lengths off the pace in third place with 100-1 outsider Schmidt bringing up the rear.
Bedrock was bought by US-based owners earlier this month but Jardine is hoping the horse remains in his stable for at least a little while longer.
"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," said the Scottish trainer.
"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."
Road To Respect fancied in Champion Chase
Noel Meade's Cheltenham Gold Cup fourth placer Road To Respect is favourite to land Saturday's Champion Chase, which is the big race at the Northern Ireland meeting.
The seven-year-old was narrowly beaten by fellow Gigginstown House Stud-owned runner Outlander in this Grade One contest a year ago.
Gordon Elliott's Outlander is aiming for a repeat success and the trainer will also saddle Don Poli with Henry de Bromhead running last season's Ryanair Chase winner Balko Des Flos and Sub Lieutenant, who won his two more recent races.
The seven-strong field is completed by Jessica Harrington's pair of Woodland Opera and Sandymount Duke.
Meade is optimistic that his favourite will perform well as he makes his first appearance of the season.
"I'm sure he'll improve, but he's fit and well and he does run well fresh," said Meade.