Never mind early-bird specials. Night-owl deals may now define Black Friday.

Retailers, jockeying for sales amid forecasts of tepid growth, opened their doors as early as 9 p.m. Thursday. And consumers, despite pessimism about the economy, came out in droves.

If the signs of an enthusiastic response are confirmed, retailers will probably continue their invasion of Thanksgiving, opening stores as some families are still polishing off their turkey dinners, analysts and company officials said.

Parking lots at Toys “R” Us stores were packed before doors opened Thursday evening. Lines snaked around Target and Best Buy locations by the afternoon, with some shoppers camping out on sidewalks since Wednesday.

Throughout the week, some store workers and families launched campaigns calling on retailers to leave Thanksgiving alone, but consumers may have shown that no time is a bad time to shop.

Knowing that there are people willing to skip turkey and stuffing for a flat-screen TV or an Xbox video game console appears to be encouraging earlier openings each year. Last year, Toys “R” Us became one of the first big-box chains to launch its Black Friday specials at 10 p.m. Thursday. This year, Walmart matched the move.

So Toys “R” Us opened its doors even earlier, at 9 p.m.

“This is just the beginning,” said Ken Homa, professor of marketing at Georgetown University’s McDonough School of Business. “Next year, we’re likely to see everybody doing this. The guys with the first opportunity to get to somebody’s pocketbook are likely to take share away from their competitors.”

Holiday sales can account for upward of 40 percent of retailers’ annual total and represented nearly 20 percent of the retail industry’s total intake last year, according to the National Retail Federation, a trade group.

Merchants entered this holiday season with the European debt crisis, weak U.S. economic growth and failed “supercommittee” talks threatening to sour consumers on spending. Some surveys show that a large number of households believe it is a bad time to spend.

Yet shoppers have a way of defying expectations.

“Consumers never cease to surprise me with how they can spend when it looks like they don’t have the ability to,” said Maggie Taylor, vice president and senior credit officer at Moody’s Investors Service.