Todd Pletcher-trained Tapwrit entered the long home straight in second place and gradually drew level with 5/2 favourite Irish War Cry, before pulling away over the final half-furlong to win by two lengths in two minutes and 30.02 seconds for the 1.5-mile distance.
The one-eyed Patch (12/1) finished a distant third in the 11-horse field at Belmont Park.
Tapwrit's victory in the third leg of the triple crown came after the colt finished sixth at the Kentucky Derby and then skipped the Preakness.
The win completed a stellar triple crown for Pletcher, who also trained Kentucky Derby winner Always Dreaming.
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Tapwrit had finished strongly in wet conditions at the Derby and proved well suited for the longer distance at the Belmont.
“The distance, I was sure he could handle it," winning jockey Ortiz said.
Pletcher described Tapwrit’s run as a "beautiful trip".
“It was everything that we had talked about,” Pletcher told NBC television. “We were hoping he had enough when it came crunch time.
“It looked like Irish War Cry still had something left (but Tapwrit) really dug down deep.
"We felt like with the five weeks in between and the way this horse had trained, we felt like we had a legitimate chance."
While the winning jockey celebrated, his brother Irad had to settle for seventh on Lookin At Lee.
Only 10 horses finished after long shot Hollywood Handsome was pulled up after breaking his irons around the first turn.
Japanese horse Epicharis was a morning scratching due to a hoof injury, missing out on a chance to secure a $1 million bonus that would have gone to the connections of the colt had he won.
(Reporting by Andrew Both in Cary, North Carolina, editing by Gene Cherry / Ian Ransom)
