Having just his second start over three miles, the Henry de Bromhead-trained eight-year-old was on something of a retrieval mission.
Despite winning a Grade One over two miles last Christmas, he made hard work of beating inferior rivals on that occasion and was put in his place on his last two outings behind Energumene at Cheltenham and Punchestown.
Ridden by Rachael Blackmore, he took a while to warm to his task but arrived on the outside going well turning in.
It was going to be a battle to the line with Kemboy and Conflated still in contention, despite the favourite Galvin dropping tamely away.
Conflated was the first to crack but Willie Mullins' old stager Kemboy would not lie down, forcing Envoi Allen to pull out all the stops before the 7/2 shot eventually claimed the prize by a length and three-quarters.
The winner is now unbeaten in four outings at Down Royal.
Robbie Power, representing De Bromhead, said: "It was brilliant. We always thought stepping up in trip would suit him. He only ran once before over three miles and that was at the end of a season.
"He didn't jump brilliant early on, he took a while to warm up to his jumping but, when Rachael wanted him later on, he was there for her.
"That opens up options for us now that he stays three miles. You'd have to think down that line (Gold Cup) anyway, he's in the King George.
"We'll get him home and see how he is after that and decide after that."
He added: "He has maintained his unbeaten record around here. It was fantastic, Henry had him cherry ripe for today. He was in proper order."
Blackmore said: "He didn't jump half as well as he can to be honest, but he was there when I needed him. He is a horse with so much talent as everyone knows. It was great that he got his head back in front here today.
"Going out Puppy (Robbie Power) reminded me that he is unbeaten at Down Royal so there was no pressure!
"He is an incredible horse. He has got so much ability and just getting it out of him is the thing I suppose.
"It's fantastic to win this race, but we are all thinking about Jack (de Bromhead) on a day like today."
She went on: "He is a funny horse. He would be lovely and relaxed and then lock on with you. I was trying to keep him switched off. We were probably getting into it a bit sooner than I wanted, but he switched off again turning in.
"Henry has done a brilliant job with him to have him right for today and it's great to win in these colours (Cheveley Park Stud) as well. They've provided me with a lot of good days and it's fantastic to ride a really big winner on this lad."