Mr Adjudicator maintained his unbeaten record over timber in the Tattersalls Ireland Spring Juvenile Hurdle at Leopardstown.
Stepped up to Grade One company after winning at the Christmas meeting at this track, Paul Townend was content to sit off the pace.
The outsider Tenth Amendment set only a steady tempo and that was to the detriment of the 4-5 favourite, Espoir D'Allen, who raced very keenly in the hands of Barry Geraghty.
Farclas, behind Espoir D'Allen on his hurdling debut, loomed up turning in but Townend was still happy to bide his time until asking for everything after the last.
The 3-1 chance, trained by Joe Murphy on the level, pulled a length and a quarter clear and is now available at around the 8-1 mark about winning the Triumph Hurdle at the Cheltenham Festival.
Townend said: "We went a fair gallop and although he's inexperienced he's tough, and when his jumping warmed up he was brilliant.
"We really didn't hang around so he had to be brave at the last, and from there to the line."
Mullins said: "It was a fantastic ride by Paul. We didn't think there'd be much pace in the race and he dropped him in lovely at the back of the field and there was actually a lot more pace than we anticipated.
"Paul was a little bit worried if he was travelling but didn't want to give him a squeeze and light him up too early.
"He held, what he thought, was a bit in hand turning in and met the last spot-on. They (Mr Adjudicator and Farclas) are two good battlers and two good horses.
"He'll run in the Triumph Hurdle next and then possibly on to the French version later on."
Gordon Elliott was pleased with the performance of Farclas and said: "It was a grand run and he's a horse for next year."
Geraghty, however, had no explanation for Espoir D'Allen's run.
He said: "It's disappointing, but there is no obvious reason. He was a bit free but I wouldn't blame that."