Shamayoun gave Paddy Brennan his first Festival winner when holding Ruby Walsh's mount Artist's Muse in the Fred Winter Juvenile Novices' Handicap Hurdle.
Brennan kicked for home at the top of the hill on Charles Egerton's runner and had the rest of the field at full stretch.
Walsh, seeking his third winner of the day on board a horse trained by his father, Ted, chased after Shamayoun but could
never get in a blow as the 40-1 shot went on to win by two and a half lengths.
Patman Du Charmil was a similar distance away third, with Gardasee fourth.
A delighted Breannan said afterwards: "It was pretty much the idea to be up there. He was more or less out on his own so I had to be pretty positive.
"It's the best feeling of my life and I was so happy with the way my horse was travelling down the hill."
