The 2/1 favourite beat 2011 Cheltenham Gold Cup winner Long Run by three quarters of a length with First Lieutenant just a further half a length back in third.
Willie Mullins' charge hit the front four out, under Davy Russell, and went clear approaching the home bend. But 11/4 chance Long Run jumped the last only half a length down and forced Sir Des Champs to produce a game victory.
First Lieutenant - a Grade 1 winner at Aintree in his last start - rallied for third at 6/1.
"That was wonderful," said Sir Des Champs owner Michael O'Leary. "The only concern is this vindicates how good a horse Bobs Worth must be. He beat them all out of sight at Cheltenham."
Morning Assembly sprung a 14-1 surprise by holding off Inish Island in the opening Grade 1 contest, the Irish Novice Hurdle.
Davy Condon's mount took the lead at the second last and secured victory by three and a quarter lengths from Mullins' 5/2 chance with Ballycasey, previously unbeaten over hurdles and sent off as the Even-money favourite, in third.
The final Grade 1 contest saw David Pipe's The Liquidator take the honours in the Champion Bumper at 4/1.
It was a sweet moment for winning jockey Jane Mangan, who was denied a Cheltenham Festival winner when Oscar Delta unseated her on the home straight during the Foxhunter Chase last month.
Gilt Shadow (12/1) followed, two and three quarter lengths back, with Apache Stronghold (16/1) third.
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- Sir Des Champs
- Willie Mullins