Nitrogen was the choice of bettors in the $2 million Breeders' Cup Distaff (G1) at Keeneland, just as Hall of Fame trainer Mark Casse had chosen her to train when he examined the D. J. Stable homebred Medaglia d'Oro filly as an unraced youngster years earlier.
Fresh off a victory in the 2022 Breeders' Cup Juvenile Fillies (G1) with Wonder Wheel, co-owner Jon Green of D. J. Stable said he and his family pondered how to reward Casse.
"We said to him, 'Do you want a bonus or do you want to pick out one of our two dozen yearlings to campaign and race?' And to his credit, he said, 'No, I want to go out and see what you have,'" Green recalled. "He didn't say no for the cash, but he said, 'What you have?' And he went out there, and he called me about 10 minutes into it, and I said, 'You get lost? Did you not make it to the farm?' And he said, 'No, no, I saw the one that I want to keep.' And I said, 'OK, who is it?' He said, 'It's the Medaglia d'Oro filly. She breathes different air.'
"And at that moment, I went ahead and went on The Jockey Club website and looked to see what elements were lighter than oxygen, and Nitrogen was available."
The filly has since been the gas.
The confidence behind that selection has been rewarded many times over, most recently Oct. 31, when the filly capped a sensational 4-year-old campaign by defeating Fully Subscribed by 2 lengths in the Distaff. The victory all but clinched a championship as older filly or mare, coming on the heels of an Eclipse Award-winning season as a 3-year-old filly in 2025.
This year brought a different end to the campaign, however. Nitrogen was only second best in the 2025 Distaff at Del Mar, no match for runaway winner Scylla, making Saturday's victory extremely satisfying for her connections.
Casse, fighting back emotion while awaiting Nitrogen in the winner's circle after the race, choked out some words, saying, "She deserved this."
She left little doubt she was superior in Saturday's race, overcoming a somewhat tardy start to stalk the pace, take the lead turning for home, and turn back a bid from her principal foe Fully Subscribed, when that filly loomed to her outside in early stretch.
But Fully Subscribed was simply second best.
"We got close to her, but just not good enough," jockey Flavien Prat said.
They met once earlier this season, with Nitrogen defeating Fully Subscribed in the June 5 Ogden Phipps Stakes (G1) at Saratoga Race Course by 12 3/4 lengths.
"My filly was a much better opponent for Nitrogen today, but she still fell short of what it takes to beat her," trainer Chad Brown said.
Though Nitrogen lugged toward the outside of the racetrack through the stretch—as is her custom—she still ran quickly, completing 1 1/8 miles in 1:48.90 on a fast track under Jose Ortiz.
"I saw (Fully Subscribed) behind me at the three-eighths pole," he said. "I drifted out a little bit in the stretch. She has a tendency to do that. But it seemed like I was clear."
She paid $3.58 to win as the favorite.
The winning connections—owner, trainer, and rider—all notched their first wins in the Distaff.
"When I asked her to go, she was full of run," Ortiz said.
Casse's second entrant Measure rallied for third, catching 2025 Breeders' Cup Juvenile Fillies (G1) winner Super Corredora, who faded to fourth after setting fractions of :23.57, :47.04, and 1:11.22.
With Saturday's victory, Nitrogen improved to 10-6-3 in 19 starts, and her earnings soared to $4,108,354. She is 4-2-1 in seven starts this year, with one of her two runner-up finishes coming when she ran second to reigning Horse of the Year and eventual Breeders' Cup Classic (G1) winner Sovereignty in the Whitney Stakes (G1) this summer.
More starts against males could be in her future. Casse said she is under consideration for the Jan. 30 Pegasus World Cup Invitational Stakes (G1) at Gulfstream Park.
"We're going to take a different path for sure this year coming up," Casse said.
Green and Casse joked that the pressure is on.
"She's out of conditions now," quipped Green, meaning allowance-race eligibility.
Beyond the thrill of owning Nitrogen, her owners took pride in breeding her. D. J. Stable bred two Breeders' Cup winners at this year's World Championships, having also co-bred Haffner with the Justify Syndicate. The latter horse was sold at auction as a yearling and went on to win the Oct. 30 Breeders' Cup Juvenile Turf (G1T) for owners Peter Brant, Susan Magnier, Michael Tabor, Derrick Smith, Westerberg, and Brook Smith and Irish trainer Aidan O'Brien.
Nitrogen, a Kentucky-bred, is one of two stakes winners produced from the stakes-placed Uncle Mo mare Tiffany Case. Her sire, longtime Darley America stallion Medaglia d'Oro, died Oct. 16 at the age of 27.
"We want to continue to watch her run. Every time she races, it's just a gift," Green said.
