The Dale Romans-trained Dullahan was promoted to the top of the betting charts at odds of 9-5 when I'll Have Another, who won this year's Kentucky Derby and Preakness Stakes, was pulled and retired because of a leg injury.
Dullahan flashed home late to finish third behind I'll Have Another in last month's Kentucky Derby and skipped the Preakness to save his energy for the last, and most gruelling, leg of the Triple Crown.
"I really wanted him (I'll Have Another) to compete. This was going to be a special race, one of the biggest races of our time. It's just devastating," said Romans.
"We're going to inherit the role as favourite, but I'd rather have him in there. I think we could have competed with him and it would have been a great race and great for the sport. It would have been something special to beat him."
Bookmakers listed Union Rags as the second choice at 3-1. Union Rags was the second favourite for the Kentucky Derby but could only manage seventh after a troubled run.
"Obviously, we have been a little disappointed," said owner Phyllis Wyeth. "But we still feel Union Rags hasn't run his race. We had some problems in the Derby ... we still think he can do really, really well, and we've switched jockeys to Johnny (Velazquez), and he just had a really nice work."
The Bob Baffert-trained Paynter was third pick at 7-2. Baffert's Bodemeister finished runner-up to I'll Have Another in the first two legs but skipped the Belmont, run over 1-1/2 miles (2,414 metres).
The only other runner in the 11-horse field under double figure odds was Street Life, who was rated an 8-1 chance.
"I feel bad for the connections, I have to be honest with you," said Kelly Breen, who won last year's Belmont with Ruler On Ice and will be represented Saturday by 15-1 shot My Adonis.
"To get so close and have something like that happen is very unfortunate. I'm sure that the fans will be disappointed, but the Belmont's the Belmont. It's still a Triple Crown race."