Soaked with sweat, Shackleford bucked and kicked until crewmen finally shoved him into the No. 5 gate at the Preakness.
One ton of horseflesh all but screamed, "Get me out of here."
Less than two minutes after the gate sprang open, the nervous colt was a cool classic winner.
Shackleford held off a late charge by the 2-1 favorite Animal Kingdom, spoiling yet another Triple Crown try and beating the Kentucky Derby winner by a half-length Saturday at Pimlico.
The chestnut colt, who led into the stretch in the Derby two weeks ago, finished the job at 12-1 odds, covering the 1 3-16 miles in 1:56.47.
With jockey Jesus Castanon aboard, Shackleford battled Flashpoint for the lead through a quick opening quarter-mile of 22.69 seconds, just a fifth of a second off the Preakness record.
They continued their duel until midway on the final turn, when Shackleford dug in to hold off the onrushing Animal Kingdom before 107,398 fans.
It was the first victory in a Triple Crown race for Castanon and trainer Dale Romans, a Louisville, Ky., native, who watched Shackleford finish fourth in the Derby.
Shackleford's pre-race antics weren't unusual. He often gets nervous and sweats excessively, not normally a good thing on a day when temperatures hit the 80s in sunny Baltimore.
"He wasn't acting that bad. It's a hot day, so that wasn't worrying me too much. I was more concerned at the quarter-pole if he was going to hold on," said Romans, who had one Breeders' Cup victory and a win in the $6 million Dubai World Cup to his credit in his long career.
"I've won some big races, but none as exciting as that one," he said, meaning the Preakness, where he finished second last year with First Dude.
Shackleford paid $27.20, $10.20 and $6.80.
Animal Kingdom returned $4.20 and $3.60. Astrology paid $8 to show.
Dialed In was fourth after finishing eighth in the Derby as the beaten favorite.
"They went fast enough early, but then they slowed out," trainer Nick Zito said. "It didn't work out."
Dance City was fifth, followed by Mucho Macho Man, King Congie and Mr. Commons. Isn't He Perfect was ninth, then came Concealed Identity, Norman Asbjornson, Sway Away, the Baffert-trained Midnight Interlude and Flashpoint.
The last horse to sweep the Derby, Preakness and Belmont Stakes was Affirmed in 1978. Big Brown was the last to attempt a Triple, in 2008.
Trainer Graham Motion, full of hope and expectation at the start of the race, looked on glumly as Animal Kingdom couldn't catch Shackleford in time.
"He ran huge. I was hoping he was going to get there," said Motion, who had kept the Derby winner at his stable 60 miles away in the Maryland countryside until race morning.
Shaking off his jitters, Shackleford broke alertly, as did another speedy horse, Flashpoint.
As they sped along, Animal Kingdom and Dialed In, the second favorite, were running at the back of the 14-horse field.
"I kind of had to hustle him out of there," said John Velazquez, riding Animal Kingdom. "We lost a lot of ground in the first turn."
Velazquez tore through multiple sets of goggles as the dirt kicked back into Animal Kingdom's face, which he clearly didn't like.
"He broke so far back the dirt started hitting him," the jockey said. "He had to make up too much ground."
Castanon was able to get Shackleford to relax into a comfortable rhythm as the pace slowed going down the backstretch. That proved to be a key moment.
"That kind of hurt us," Motion said. "That middle quarter really affected the outcome of the race."
Midway through the final turn, Flashpoint gave up, leaving Shackleford as the lone target for the closers. Animal Kingdom started to pick up the pace entering the final turn. Unlike in the Derby, he couldn't find a clear path and Velazquez had to pick his way around traffic to get to the outside.
"I can't believe what Johnny weaved through the last three-eighths of a mile," Motion said. "But he was coming and coming. I'm not sure what is better, if we were that close or to be beaten further."
At the top of the stretch, Animal Kingdom emerged as the main threat to Shackleford. He passed horses in pursuit of the leader while Astrology made a strong run along the rail.
"I felt somebody coming at the sixteenth-pole," Castanon said. "I knew that Animal Kingdom was the only horse who was able to come get me."
He and Astrology had Shackleford in their sights, but the winner refused to give up through the long run to the finish line.
Shackleford's victory, along with his participation in the Fountain of Youth Stakes and a top-three finish in the Florida Derby, netted bonuses for the owners and trainer.
Michael Lauffer and W.D. Cubbedge walked away with $1.1 million, including the $600,000 Preakness winner's purse and a $500,000 bonus. Romans earned $50,000 in bonus money.
The biggest bonus went unpaid. Dialed In could have won $5.1 million if he had finished first, including $5 million for running in the Holy Bull Stakes and winning the Florida Derby.