At 8 pm, the 30-year-old teacher from Ireland raced into the store, arms linked with her sister-in-law, as shoppers cheered and employees stared.
"Anything that's on sale that we can fit in our suitcases we're going to buy," said McCormack, who came to New York with empty luggage to fill with new purchases. "The rest of the family is out to dinner. They think we're mad," she said.
While most in the United States spent the day bonding with friends and family over turkey dinners and football games, some were enticed by big discounts and open stores to begin their holiday bargain-hunting a day earlier than the traditional "Black Friday" sprees that follow Thanksgiving.
With six fewer shopping days this year than in 2012, Macy's and a slew of other stores opened on Thanksgiving for the first time in a bare-knuckle brawl for a bigger slice of holiday sales.
Macy's was packed, and overall online sales for the day were up an estimated 11.5 percent over last year, according to a report at IBM Digital Analytics Benchmark.
But many shoppers interviewed by Reuters were being careful and buying only one or two items.
"I'm coming in for the TV, and that's it for today," said Ioannis Gomez, 20, of Westbury, Long Island as he waited outside a Best Buy Co Inc which had provided shoppers with blue hats and scarves bearing the retailer's logo.
Many forecasters expect overall sales growth to be tepid in a season plagued by shaky consumer confidence and given that there are few fashion must-haves.
"The ones that are opening earlier are going to get more sales, but in the end, I don't think the overall pie gets any bigger. It's just a share gain," said Brian Yarbrough, a retail analyst with Edward Jones.
EARLIER OPENINGS, HOLIDAY PAY
With deals on offer before Thanksgiving tables were even set on Thursday, some disagreed with the retail industry's approach. Critics circulated online petitions, and a handful of franchise owners said they had defied corporate orders by keeping their stores closed.
Target Corp, Best Buy and Toys "R" Us Inc opened earlier on Thursday than they did last year. Many Wal-Mart Stores Inc U.S. locations were open all day, with Thanksgiving specials beginning at 6 p.m.
Department store chains Kohl's Corp, J.C. Penney Co Inc and Macy's all announced earlier this year they would open on Thanksgiving Day for the first time.
Retail analyst Yarbrough estimates that overall sales for November and December will be up 2.8 percent. That is a more conservative view than the 3.9 percent jump forecast by the National Retail Federation.
The profit on those extra sales will depend on whether the eye-catching bargains are margin-squeezing loss leaders, analysts said.
SHOPPERS EAGER FOR SALES
Manny Ramirez, 25, was first in line at the Best Buy in Iselin, New Jersey. For about $435, he bought a 39-inch TV, an Apple Inc iPod Nano music player and an Amazon.com Inc Kindle e-reader - and nothing else. "I did my homework and knew what I wanted to get," he said.
Another shopper, Rohit Kumar, 33, emerged from the store with just a small blue bag - he bought just a Microsoft Corp XBox 360 videogame console and a Google Inc Chromecast digital media player. He had arrived at 6 p.m. and only had a 10-minute wait to enter the store. He was checked out by 7:15 p.m., and said he saved about $75 total.
Some say retailers' fortunes depend a lot more on wealthier shoppers who have benefited from rising share and home prices this year.
"There are two sides to the story. If you look at households with over $100,000 of income, those folks are going to spend twice as much as people of incomes under $100,000," said FTI Consulting's Steve Coulombe.
At Macy's flagship store in New York, five hundred employees were expected to work Thursday night. Many appeared shocked when the doors opened and thousands of shoppers flooded in.
"This is madness," said Sharon, a store employee who declined to give her surname. "We are expecting one million people," she said. "We don't get trained for this."