The party began at the trainer's barn at Churchill Downs, moved to a charity dinner and ended up at a downtown hotel where the colt's owner, J. Paul Reddam of Windsor, Ont., had reserved the 25th floor for about 100 people.
As O'Neill walked to his room, he saw dozens of morning newspapers lining the hallway. The bold black headline blared, "I'll Have Another!" with a huge photo of the chestnut colt edging past Bodemeister to win the Derby by 1 1/2 lengths.
"Whoa, that really was an unbelievable feeling," the trainer said. "That was another stamp that it really happened."
O'Neill isn't wasting any time in sending I'll Have Another to Maryland for the second leg of the Triple Crown. The colt will fly from Louisville to Baltimore on Monday, making him the earliest arriving Derby winner since Monarchos showed up at Pimlico four days after his 2001 win.
I'll Have Another is in position to win horse racing's first Triple Crown since 1978 when Affirmed swept the Derby, Preakness and Belmont Stakes within a five-week span.
"I get goose bumps just thinking about it," O'Neill said. "I think he is the kind of horse who can maintain his form and keep it going."
I'll Have Another likely will be seeing some of his old rivals again in Baltimore.
Seven Derby horses might run in the 1 3-16-mile Preakness, led by runner-up Bodemeister. The other possibilities are Went the Day Well (fourth), Creative Cause (fifth), Liaison (sixth), Union Rags (seventh), Hansen (ninth) and Optimizer (11th). Went the Day Well sustained a cut on his right front ankle in the Derby, but trainer Graham Motion said it wasn't a problem.
Seven new candidates are on tap, too.
They are: Pretension and Brimstone Island, the top two finishers in the Canonero II Stakes on Saturday at Pimlico; Cozzetti; Hierro and Paynter, the top two finishers in the Derby Trial at Churchill; Jerome Stakes winner The Lumber Guy; and Tiger Walk.
O'Neill, based at Betfair Hollywood Park in Inglewood, Calif., last ran a horse in Maryland six years ago when Thor's Echo won the Grade 1 De Francis Memorial Dash on his way to winning an Eclipse Award as the nation's top sprinter. Reddam has owned one previous Preakness starter — Wilko, who was 12th in 2005.
O'Neill plans to briefly return to California before heading back East this week. He told his young son and daughter that if I'll Have Another won the Derby, the family would get a hot tub.
"We are going to have to do some shopping now," he said.
Five-time Preakness winner Bob Baffert plans to keep his two Derby runners, Bodemeister and Liaison, along with Paynter, at Churchill before deciding next weekend whether to take on I'll Have Another in Baltimore.
"I will let him tell me if he's ready, like I did with Lookin At Lucky," Baffert said about Bodemeister, who led most of the Derby until getting caught late by I'll Have Another.
In 2010, Lookin At Lucky finished sixth as the Derby favourite and went on to win the Preakness.
"With Lookin At Lucky, the day after the Derby I told them, 'We're not going to run,'" Baffert said. "The next Monday I said, 'Not only are we going, we're going to win this.' I've got to wait and see if he shows me a spark."
Four of the top six places in the Derby went to horses based in Southern California. Besides I'll Have Another and Bodemeister, Creative Cause was fifth and Liaison was sixth.
Trainer Michael Matz said he didn't think seventh-place Union Rags, second choice in the Derby betting, would try the Preakness. The colt is based in Fair Hill, Md., about 1 1/2 hours from Pimlico. However, Matz said running in the 1 1/2-mile Belmont on June 9 "would make more sense."
Matz said he would decide after watching Union Rags train and talking with the colt's 71-year-old owner Phyllis Wyeth.
Union Rags broke a step slow, then got bumped and squeezed back to 18th in the 20-horse field before hitting traffic on the far turn. Matz said he felt badly for the horse and his owner.
"I don't mind getting beat, I just don't like getting beat the way he did in the Florida Derby and the Kentucky Derby," Matz said, referring to Union Rags' third-place finish in Florida as the favourite. "I know I shouldn't be crying over spilled milk because it's happened to other people, too."