Mavis L. Wanczyk won the $758.7 million Powerball prize, the biggest undivided lottery jackpot in U.S. history

A 53-year-old Massachusetts hospital worker stepped forward Thursday to claim the biggest undivided lottery jackpot in U.S. history a $758.7 million Powerball prize after breaking the news to her employer the way the rest of us only dream of- “I called and told them I will not be coming back.”

“The first thing I want to do is just sit back and relax,” Mavis L. Wanczyk told reporters at a news conference.

Ms. Wanczyk chose to take a lump-sum payment of $480 million, or $336 million after taxes, lottery officials said. Winners who take a gradual payout stand to get more money spread out over several decades.

Even after paying taxes on the winnings, Wanczyk is worth more than some small countries such as Micronesia, which has a gross domestic product of $322 million, or the Pacific islands of Palau, with a GDP of $293 million, according to 2016 figures from the World Bank.

The previous evening, she recalled, she was leaving work with a firefighter and remarked, “It’s never going to be me. It’s just a pipe dream that I’ve always had.”

Then she read the number on her ticket and realized she had won.

Ms. Wanczyk worked for 32 years in a clerical job in the nursing department at Mercy Medical Center in Springfield, the hospital said.

About a month ago, she shared a post on Facebook joking that she needed a vacation. “And by ‘vacation,’” the post read, “I mean I need to move away and find a new job. On a beach. With rum.”

The jackpot is the largest ever won with a single ticket. It is the second-largest U.S. lottery prize, ahead of a $656 million Mega Millions prize won by three people in 2012. But Wednesday’s big prize is still dwarfed by a $1.6 billion Powerball jackpot divvied up between three winners in January 2016.

Ms. Wanczyk has two adult children, a daughter and a son.

Massachusetts Treasurer Deb Goldberg said she offered advice to the family about being careful with their newfound wealth.

“A lot of people will be coming at them with all sorts of things,” Goldberg told reporters. “I highly encourage them to find very, very good lawyers and advisers and think very, very carefully about how they are going to manage their assets.”

Ms. Wanczyk bought a total of five tickets. Two were computer-generated Powerball tickets, and three used numbers that she chose. The winning ticket, she said, was one with numbers that used family birthdays.

The announcement that a winner had come forward came after a turbulent morning in which lottery officials initially misidentified not only the store that sold the winning ticket, but the town.

The lottery corrected the site where the single winning ticket was sold to Chicopee, Massachusetts. Overnight, it had mistakenly announced the winning ticket was sold at a shop in Watertown, just outside Boston.

But shortly before 8 a.m., the lottery said it had made a mistake, and that the winning ticket was sold at the Pride Station & Store in Chicopee, about halfway across the state.

Massachusetts Lottery Executive Director Michael Sweeney said officials were manually recording the names of the retailers that sold the winning ticket and transcribed it incorrectly. Sweeney issued an apology for the confusion created by the error, but said lottery staff remained thrilled that a jackpot winning ticket and two $1 million winning tickets were sold in Massachusetts one of those at the Watertown location.

Mike Donatelli, a spokesman for the Pride Station & Store in Chicopee, said the store was notified shortly before 8 a.m. that it had actually sold the record jackpot ticket.

Mr. Sweeney said the store will pocket $50,000 for selling the jackpot winner. Bob Bolduc, owner of the Pride store chain, said the proceeds would be donated to local charities.

“The phone started ringing at 8 o’clock” Bolduc said. “We were as surprised as everybody else. We’re happy for our customer, and we’re happy for the charities.”

The lucky numbers from Wednesday night’s drawing were 6, 7, 16, 23 and 26, and the Powerball was 4.

Powerball is played in 44 states plus Washington, D.C., Puerto Rico and the U.S. Virgin Islands, all of which collectively oversee the game. Drawings are held twice a week. Five white balls are drawn from a drum containing 69 balls and one red ball is selected from a drum with 26 balls. Players can choose their numbers or let a computer make a random choice.