Big Buck's created history by winning his third straight Ladbrokes World Hurdle under Ruby Walsh.
In what was by far the biggest battle he has faced, Walsh decided to keep his mount close to the pace in a change in tactics to previous years.
Tom Scudamore played the waiting game on his big market rival Grands Crus and Big Buck's (10-11 favourite) jumped the last with a one-length advantage.
The gap narrowed halfway up the running, but Grands Crus began to flatten out inside the final 100 yards as the Paul Nicholls-trained stayer retained his crown by a length and three-quarters.
Big Buck's becomes the first horse ever to win the race for a third consecutive year.
Cross Kennon took the field along through the early stages but they were not going a serious pace.
Walsh was in the right position, however, as he was never more than two lengths off the speed.
Cross Kennon was still in front turning into the straight, but Walsh was the first to commit on Big Buck's.
Fiveforthree and Mourad also briefly looked dangerous but it was Grands Crus who emerged as his biggest danger - only for Big Buck's to find more up the hill.
Mourad took the minor honours in third, another two and three-quarter lengths away from the undisputed champion.
Walsh said: "He's an aeroplane, but I made a bad mistake as I dropped my stick halfway to the last hurdle.
"It was my own fault as I was trying to see where the others were behind me so I was only half-watching what I was doing.
"I knew I had loads of horse left, but I knew it was going to be tactical and that Grands Crus was going to try to follow me.
"This horse has matured so much mentally you can stretch him in front and he has dug deep.
"He had an entry in the Arkle but I've always thought he could run a big race in the Champion Hurdle.
"I was lucky enough to get away with it today.
"He's a wonderful horse and he's got me out of trouble."
Walsh added: "In a hurdle race he's just as unbeatable as they come - he's like (American great) Cigar on the Flat.
"The guys riding against him knew exactly what to do and had their tactics spot-on, but it didn't matter.
"He's just different, he has so much class as you're riding a Champion Hurdle-Gold Cup horse in a stayers' hurdle."
Nicholls said: "We were a bit worried about the ground and that they weren't going to go a gallop.
"We knew pretty well what Grands Crus was going to do.
"We just improvised a little bit. I was nervous as he hasn't run on that ground. He wins by staying, and class is what he's got.
"David (Pipe) was the first to shake my hand. He's a great fellow. The best horse won on the day but it was an awesome performance by both horses.
"I think that's arguably Big Buck's career best."
Owner Andy Stewart added: "We are thrilled. Ruby was as cool as a cucumber."