Life Of A Lord, in the lead for most of the way and avoiding virtually all the mishaps, came home unchallenged at 12-1 in the hands of Trevor Horgan with stablemates Kelly's Pearl (16-1) and Loshian (6-1) completing the unprecedented clean sweep.
British-based jockeys were not so fortunate. Graham Bradley, just back in action after his serious ear injury sustained at Aintree, was trampled on by several of the field after Kim Bailey's Mr Jamboree crashed at the first fence.
Next time round at the downhill fence past the stands it was the turn of the hot favourite, Postage Stamp, to exit under Mark Dwyer, and then both Richard Dunwoody aboard Bishops Hall and Philip Hide on Natalies Fancy were brought down starting out on the final circuit as a loose horse careered straight in front of them.
Graham Bradley was treated on the track before being taken to hospital for X-ray examinations on a shoulder and his ribs.
O'Brien said: "I told my three jockeys to ride the horses as they found them. It is incredible that they managed to survive and come home together at the head of the field."
Trevor Horgan was given the mount on Life Of A Lord when champion Charlie Swan rejected the nine-year-old in favour of the eventual third Loshian.
Dunwoody had better luck earlier in the afternoon when Dermott Weld's Blazing Spectacle landed the odds in the opening Digital Hurdle in the colours of Michael Smurfit.Reuse content