The Barry Geraghty-ridden seven-year-old (12-1) found just a little more when it mattered to take the Grade One by a neck for the Rebecca Curtis team.
Irish challenger Morning Assembly finished third.
Corrin Wood made most of the running, but his challenge weakened at the top of the home straight once the pace accelerated.
Several horses came to grief as a consequence of the heightened tempo, but Ballycasey, the 13-2 joint-favourite, appeared in a vigilant mood as he was nudged into the lead three fences from home.
Ruby Walsh’s companion suddenly began to tread water, though, as fellow market leader Smad Place leapt purposefully towards the head of affairs two out.
But O’Faolains Boy was never far away, and a crisp jump at the last then put Geraghty in pole position.
An absorbing tussle ensued, but Curtis’ inmate grasped the moment with a lunging drive inside the final 150 yards.
Geraghty said: “He just ran in snatches a little bit. He didn’t jump as well as he did in Ascot. I was never happy and never thought I’d win,but in the last mile he started to come alive a little bit. He got there, slightly under sufferance.
“There’s improvement in him. He didn’t feel as good today as he did at Ascot for some reason and he didn’t sparkle, but he’s still won.”
Curtis said: ``It's amazing to get another winner at the Cheltenham Festival.
“Before Christmas our horses weren’t running great, but they are now and we knew he was very well coming here.
“He twisted his shoe quite badly but it didn’t stop him in the end.
“He’s a funny horse, he finds a wind then goes again.
“He proved he was a nice horse last year over hurdles but this season hadn’t been ideal with him.
“It’s not a massive surprise as he proved at Ascot he was decent but you never expect to win here.
“Everyone wants a Gold Cup horse, and you never know, if he keeps progressing he might be one day.
“The Gold Cup next year would be the dream.”
Smad Place’s trainer Alan King said: “We’ve got beat by a better horse, but I’m thrilled with him.
“We always hoped be as good a chaser as he was a hurdler and he’s going that way. The ground drying out was not a problem for him.
“Of course, I’d have loved to have won, but he did great.”
Pat Fahy, trainer of third-placed Morning Assembly, said: “It was a rough enough race and he got into a bit of bother, but I’m delighted with the run in the circumstances.
“It was only his fourth run over fences and it was very quick ground but he stayed very well and his heart got him to finish where he did.
“Davy (Russell) said he’d never ridden in an RSA when they’d gone so quick. He’ll go to Punchestown now.”