"Honestly, the whole thing went by so fast, and I feel like I'm in a different reality right now," the Bel Air native said after winning in 4 minutes, 9.54 seconds, the second-best time in the world this year.
Ryan Lochte, the 2012 Olympic gold medalist in the event, finished third. He said he pulled his groin in the morning preliminary, which forced him to go out faster than he wanted to in the evening, because he knew he wouldn't be able to use his legs properly on the breaststroke leg.
The breastroke proved decisive as Kalisz erased Lochte's three-second advantage and snatched a lead he would hold throughout the finishing freestyle leg. His Georgia teammate, Jay Litherland, finished second and also earned an Olympic berth.
"Any U.S. swimmer that makes it, it's an amazing swim," Lochte said, clasping hands with Kalisz after the race. "He's definitely one of the guys we need in that 400 IM."
The proud legacy of the North Baltimore Aquatic Club, where Kalisz learned his craft, is entwined with the 400 IM, a race that demands the very traits coach Bob Bowman emphasizes—mastery of all strokes and a deep base of fitness.
Phelps owned the race during his Olympic conquests in 2004 and 2008. So it was no small thing for Kalisz to seek his first Olympic berth in that event, with Phelps looking on from the NBC broadcast perch.
Phelps — who revealed that he will not swim the 200-meter freestyle Monday at trials — celebrated his friend's victory by thrusting both fists in the air.
"I'm so happy for Chase," Phelps said. "I was crying when I was hugging him. For him to be able to do that was a very special moment for me, and we kept the 400 IM in the NBAC family."
"He told me he was proud of me, and that was just a very emotional moment," Kalisz said. "He's been the one guy I've looked up to my entire life.'
Though Kalisz, 22, is a terrific all-around swimmer in his own right, his rise in the sport has been that of a little brother, always trying to catch up.
When he first hit the pool in Harford County, the target was his older sister Courtney, who qualified for three events at trials the summer after she finished eighth grade.
Once he joined the family parade to NBAC, he shifted his gaze to an even greater target — Phelps.
Phelps thought of Kalisz as little more than a scrappy kid who liked to spin the rims on his Cadillac Escalade in the parking lot of the Meadowbrook Aquatic Center. But eventually, he noticed the way the kid tried to beat him in every single practice race, no matter how mundane.
Sensing a kindred spirit, Phelps adopted Kalisz as a brother. Which meant he hounded and mocked him relentlessly.
Phelps, who learned from the Michael Jordan school of motivation, has always lashed teammates with a sharp tongue in practice. But none more so than Kalisz, whom he saw as a potential successor to the 400 IM throne.
"I'm very hard on him," Phelps said. "I just see potential, and I want him to be the best he can be."
He said at one point, Kalisz asked Bowman to have him back off.
Kalisz said that after years of being shaped in the heat of the Phelps kiln, nothing shakes him on competition day.
"I've learned tons from Michael," he said. "Stuff that Bob couldn't teach me. If I wasn't doing something right, he would always tell me. And it means more coming from a guy who did it."
Kalisz's body didn't mature until after his senior year of high school, when he suddenly added 15 pounds of muscle and became a threat at the highest levels of international competition. He won a silver medal in the 400 IM at World Championships in 2013 and set an American record in the 400-yard IM the next year.
His performance dipped in the second half of 2014 and 2015 as he coped with the expectations associated with success. After his disappointing 2015 season (he did take a bronze medal in the 400 IM at last summer's world championships), Kalisz took a redshirt year from Georgia and moved to Arizona to train full time with Bowman and Phelps.
This year, he's spent 10 weeks training at high altitude in Colorado and said he hasn't missed a single one of Bowman's famously rigorous workouts.
These days, he's as likely to take it to Phelps in practice as vice versa.
Bowman was bullish on Kalisz's form as trials loomed, saying, "He's exactly where I had hoped he would be."
When Phelps comes to trials, he's used to swimming the 400 IM rather than watching it in street clothes. But even as an observer, he was intrinsic to the plot of Sunday's race, which pitted his protege against arguably his greatest rival.
It was Lochte who dusted Phelps in the 400 IM final at the 2012 Olympics, demonstrating that Phelps was no longer quite the multi-event monster of his prime.
Lochte, however, came to this year's trials as a 31-year-old, thought by some to be biting off more than he could chew by swimming the grueling 400 meters.
Phelps warned him not to swim the race if he wasn't fully conditioned for it. "There is no way to hide from that race," he said, speaking from experience.
But Lochte has always thrived on daunting workloads, and he seemed jazzed by the prospect of taking on the younger Kalisz. They thrilled the crowd with their head-to-head duel in a morning preliminary, which Kalisz won by a smaller margin than the evening final.
Now that Kalisz has his Olympic spot, he can enjoy the rest of the week. He's entered to take on Phelps in the 200-meter IM and 200-meter butterfly and also to swim the 200-meter breaststroke. He won't be favored in any of those events but projects as a contender for the final in each. His younger siblings, Connor and Cassidy, will also swim at trials.
The next challenge for Kalisz will be to lower his time further in Rio. Japan's Kosuke Hagino swam the race in 4 minutes, 8.85 seconds in May and his teammate, Daiya Seto, won the World Championship in 4 minutes, 8.5 seconds last summer.
Kalisz has never broken 4 minutes, 9 seconds.
Phelps told his friend the mark he predicts will win in Rio and said he thinks Kalisz has the potential to go faster.
"Those guys are awesome, and I've got to improve what I just did there to be competitive with those guys," Kalisz said of the Japanese. "Those guys are certainly the two best in the world, and they're the favorites, so I've got to be sharp going into Rio."