At Washington University in St. Louis, Clifford Goldkind played poker and majored in game theory and economics.

The two interests played off each other, he said — the major taught him about behavioral psychology and decision-making under pressure, knowledge he used when playing his favorite game.

Those lessons came in handy for the Potomac resident this month.

Goldkind won $559,514 on June 11 at the World Series of Poker in Las Vegas, defeating a field of 2,302 players in Texas hold ’em. The 24-year-old also won his first World Series bracelet, the nonmonetary prize coveted by poker players.

“I couldn’t lose,” he said.

He attributes his victory to a mixture of luck and strategy, but in the end, he said, “it was all about the decision-making” he’d learned in college.

Staged at the Rio All-Suite Hotel and Casino, the World Series began May 27 and runs through July 16. This year, the tournament offered about 50 events. The 43rd annual competition drew experienced players from such countries as the Netherlands, Belgium and Brazil.

The World Series is open to anyone older than 21 who can pay the $1,500 buy-in; amateurs and celebrities alike participate in the competition, which is owned and organized by Harrah’s Entertainment.

Goldkind’s path to the series began after his college graduation in 2009. He enlisted in the Israel Defense Forces through Mahal, an organization for overseas volunteers, but he had almost a year between graduation and the beginning of his service in the army. He spent the time playing poker online, a hobby he had picked up in high school.

During those months, and during much of his time in Israel, poker was his income.

“It wasn’t stressful,” he said. “There were unlucky times, but it was great. That was when I really learned strategy.”

Goldkind’s victory thrilled his family, who watched the World Series at home, as well as his friends, who attended the event.

Although the friends had been playing in other events, by the end of Goldkind’s three-day event, they stayed to watch him.

“Normally, I wouldn’t stand and watch someone play poker, because it can get boring,” said Danny Drew, who watched Goldkind play for 10 hours. “But he was doing really well, so I stayed and watched him take pot after pot. It was unbelievable.”

Drew and Goldkind met in college, where both played poker with friends.

“He was a very good player coming in,” Drew said. “I used to win all the time, but the day he came to our group, he and I won all the money. And I was like, ‘We’re either going to be rivals or friends.’ ”

Luckily, he said, the pair became close friends, sharing their winnings and discussing strategy.

“We study poker, talk poker, and go over our hands together to make sure we played them right,” Drew said.

That focus on strategy proved invaluable to Goldkind, who was competing against such famous poker players as Barry Shulman and Sam Stein.

“With the list of poker greats Clifford had to face, it would be an understatement to suggest [his win] was a little unexpected,” series representative Harry Hammel said in an e-mail.

At the series, Goldkind played 35 hours of poker in three days. He and Drew woke up at 10 a.m. each day and went to the Rio, where they bought energy bars, carrots and lots of water. During the tournament-wide dinner break, Goldkind avoided “greasy, heavy foods — anything that would make me fall asleep at the table,” he said.

Each day, he played from around noon until well past midnight.

“It was pretty grueling,” he said.

Before his victory in Texas hold ’em, Goldkind was having little success at other series events. But when his luck changed for the better, the other, older players were surprised but congratulatory, he said.

He was rather excited himself.

“I yelled,” he said. “My friends, who had been watching from the bleachers, hugged me and we screamed.”

Goldkind began playing poker in high school “on a very surface level,” he said. “It was when poker got big, when that was what all the guys were doing.” He learned the rules of the game from his friends and from watching the World Series on ESPN.

Goldkind dreams of supporting himself by playing poker, leaving him free to think about things other than making money. He’ll attend the Fletcher School of Law and Diplomacy at Tufts University in Massachusetts this fall and said he hopes to work in microfinance or international development policy, perhaps creating a private equity firm to aid developing countries.

Sara Goldkind supports her son’s plan.

“I’m fine with it,” she said. “Clifford has plans to do other meaningful things. He’s very idealistic.”

Goldkind’s advice for another amateur players in his shoes?

“Don’t be focused on winning, or on how much you can win,” he said. “You should just be concentrating on playing the game.”