Supasundae landed the Coral Cup for trainer Jessica Harrington and jockey Robbie Power.
Owned by Alan and Ann Potts, the 16-1 chance came into his own approaching the final flight and was much too good for Taquin Du Seuil, who succumbed by two lengths.
Who Dares Wins and Monksland finished third and fourth respectively.
Power said: "He's galloped all the way to the line.
"He was a very, very good bumper horse and beat Yanworth in the (Aintree) Bumper.
Harrington said: "I only inherited him this year from Henry de Bromhead so it's absolutely fantastic.
"Good ground was the real making of him. We knew he'd improve a real lot on that ground."
Tombstone, the 7-2 favourite, was most disappointing.
1450 Coral Cup Handicap Hurdle (Grade 3) result— RTÉ Racing (@RTEracing) March 15, 2017
1 Supasundae 16/1
2 Taquin Du Seuil 12/1
3 Who Dares Wins 33/1
4 Monksland 66/1
Cause Of Causes claimed the third Festival success of his career with a tremendous display in the Glenfarclas Chase.
Having won the National Hunt Chase in 2015 and the Kim Muir 12 months ago under Jamie Codd, the combination were among the market leaders for this cross-country event at 4-1.
French raider Amazing Comedy led to the second-last, but was soon swamped by a trio of JP McManus-owned runners and Bless The Wings.
Gordon Elliott's Cause Of Causes picked up to lead at the final obstacle and galloped up the hill for a nine-length success over stablemate Bless The Wings.
Cantlow, the 9-4 favourite, was third ahead of Auvergnat in fourth.
Elliott said: "He seems to come well at Cheltenham every year.
"He's an absolute superstar and we love him to bits. Jamie also gave him a great ride.
"It was a great result as we also had the second.
"If you have a plan, you have to try and do it right.
"We've had an unbelievable week. It's been a dream come true."
4.10 Glenfarclas Chase (Cross Country Chase) result— RTÉ Racing (@RTEracing) March 15, 2017
1 Cause Of Causes 4-1
2 Bless The Wings 10-1
3 Cantlow 9-4F#CheltenhamFestival
Nick Williams gained his first Cheltenham Festival winner as Flying Tiger ran out a 33-1 victor in the Fred Winter Juvenile Hurdle.
The well-fancied Divin Bere moved smoothly towards the front end rounding the home turn before being joined by Nietzsche at the final flight.
However, it was Flying Tiger who finished best, getting up to beat Divin Bere and provide champion jockey Richard Johnson with his first winner of this year's Festival.
Nietzsche was third ahead of Project Bluebook in fourth.
Johnson said: "It's fantastic. Lizzie Kelly was riding another horse (Diable De Sivola, fifth) but has done a lot of work to get him settled.
"He's always been talented in France but he got it right on the day.
"I'm slightly speechless."
4.50 Fred Winter Juvenile Handicap Hurdle (Grade 3) result— RTÉ Racing (@RTEracing) March 15, 2017
1 Flying Tiger 33-1
2 Divin Bere 9-2F
3 Nietzsche 12-1
4 Project Bluebook 14-1
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