A lucky $18 (£13) bet on the winning horse from the Kentucky Derby led to a woman from the US state of Texas walking away with $1.2m.
Margaret Reid's betting haul this weekend made her almost as successful as the winning horse, Justify, whose owners collected $1.4m.
Ms Reid won a "pick five" bet where she had to bet on five horse races, of which the Kentucky Derby was the last.
After treating herself to a holiday, Ms Reid plans to invest her new wealth.
"It was a big ticket because it was a couple of long shots in the middle of it," she told a CBS News affiliate.
Congratulations to our biggest winner! Her $18 wager won her 1.2 million! pic.twitter.com/jVYXLCIs4g— Retama Park (@RetamaPark) May 5, 2018
"It was an amazing feeling yes, that you won a really big, like a really big ticket. A mini-lotto if you will."
Ms Reid, a longtime horse-racing fan, said she carefully analysed the odds when she made her "pick five" bet.
She had to choose the winning horses of five consecutive races to achieve her million-dollar win.
"I understand the programme and I can break down the races," she said.
"It doesn't always work out, but sometimes it does."
The Derby-winning horse had good odds beforehand, 3-1, but in one of the other races Ms Reid shrewdly picked a horse with 40-1 odds of winning.
After her holiday, Ms Reid told CBS some of her winnings will go towards her daughter's college education.
The Kentucky Derby is the most popular horse race in the US, as well as the longest running sporting event in the country.