Justify has won the 150th running of the Belmont Stakes, becoming the 13th horse in history to win the Triple Crown. Trainer Bob Baffert has now won two Triple Crowns in four years.

The 3-year-old colt improved to 6-0 in its racing career that began in February. Seattle Slew was unbeaten when he won the Triple Crown in 1977.

Sent off as the 4-5 favorite, Justify went to the lead out of the starting gate and led nine rivals around the track's sweeping turns on Saturday. He's the first Triple Crown winner to face that many rivals in the 1½-mile Belmont.

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Justify began his racing career on Feb. 18, a scant 77 days before the Kentucky Derby. He won his first three races by a combined 19 lengths, making trainer Bob Baffert a believer.

The chestnut colt burst onto the national scene with a 2½-length victory on a sloppy track in the Derby. Two weeks later, he survived a challenge in the Preakness, winning by a half-length, again in the slop to set up a Triple Crown try.

On an 80-degree day at Belmont Park, Justify was a cool customer.

He didn't flinch when greeted by a roaring crowd as he walked onto the track. He stood so quietly in the starting gate that jockey Mike Smith wondered if he'd respond when it sprang open.

Did he ever.

Justify led all the way in achieving one of the sports world's toughest feats 45 years to the day that Secretariat won the Belmont by a record 31 lengths. Justify accomplished a lot in a very short time.

Jockey Mike Smith reacts atop of Justify #1 the 150th running of the Belmont Stakes at Belmont Park on June 9, 2018, in Elmont, New York. Getty

At 6-0, he's the second undefeated Triple Crown winner; he's the first to sweep the Kentucky Derby, Preakness and Belmont without racing at age 2; and he's the only horse to beat nine rivals in the Belmont with a Triple try on the line.

His human handlers also made history.

Baffert became the second trainer to win the Triple Crown twice. He did so with American Pharoah in 2015, ending a 37-year drought. James "Sunny Jim" Fitzsimmons guided Gallant Fox in 1930 and Omaha in 1935.

"It never gets old," Baffert said. "American Pharoah, he'll always be my first love."

At 52, Smith became the oldest jockey to win the Triple Crown. Justify's victory gives racing its second Triple Crown winner of the decade. The last time there were two Triple Crown champions in the same decade was the 1970s, which produced Secretariat, Seattle Slew and Affirmed.

The powerful colt with the blaze running the length of his face showed no signs that the rigors of running a compressed schedule had gotten to him.

On a fast, dry track, Justify was just as good in his third race in five weeks at his third different track. Sent off as the 4-5 favorite, Justify ran the longest race of the series in 2:28.18 and paid $3.60, $3.50 and $2.80.

"This horse ran a tremendous race, he's so gifted," Smith said. "He's sent from heaven. I tell you, it's just amazing. I can't describe the emotions that's going through my body right now."

Justify becomes the thirteenth Triple Crown winner and the first since American Pharoah in 2015. Getty

Baffert had fretted after Justify drew the No. 1 post, a spot he detests for his horses. But Smith turned it into an advantage, gunning Justify to the lead and defying any horse to challenge.

Restoring Hope, also trained by Baffert, ran interference for the champion while traveling second and deterring any threats by forcing them to go extremely wide. Nobody did.

Smith got the big colt into a relaxed rhythm under a moderate pace heading into the backstretch, and he had an easy trip from there.

There were mild bids turning for home. Vino Rosso made the most serious move to get within a length but never threatened. Justify pulled away down the 1,097-yard stretch in front of a grandstand packed with screaming fans with only 24-1 shot Gronkowski picking up the chase down the lane.

Gronkowski, named for and partly owned by New England Patriots tight end Rob Gronkowski, returned $13.80 and $7. Hofburg paid $3.70 to show.

Vino Rosso finished fourth, followed by Tenfold, Bravazo, Free Drop Billy, Restoring Hope, Blended Citizen and Noble Indy.