Add the nation’s two biggest retailers to the list of those that will open their doors earlier this Thanksgiving than ever before.

Target said Monday that it will let in shoppers at 8 p.m., an hour earlier than last year. And Wal-Mart will move up its opening to 6 p.m., two hours earlier than in 2012.

They follow Macy’s, Kohl’s, Best Buy, Sears and others in announcing plans to kick off the traditional Black Friday shopping rush in the evening hours of the holiday itself.

Last year, millions of shoppers took to the aisles on Thanksgiving, despite grumbling from some store employees and customers about intrusion on the holiday. For this holiday, many retailers are opening even earlier, as they aim to fight online competition while building momentum for what they hope will be a strong weekend of selling right through Cyber Monday.

“By offering advance access to deals at and opening our stores earlier, we are making it easier for guests to build a Black Friday ritual that works for them,” said Kathy Tesija, the Minneapolis-based company’s executive vice president of merchandising and supply chain.

Big-box retailers are trying to satisfy everyone with a wide variety of deals all weekend long through Cyber Monday. Consumers and some analysts are already speculating that the earlier openings will dilute Black Friday spending, but retailers are staking out their territories by offering doorbusters on both days.

Both Target and Wal-Mart will be selling an iPad mini W-Fi 16 GB for $299 plus gift cards of $75 to $100 with purchase. Wal-Mart will be offering a 32-inch LED TV for $98. Last year, a similar TV was $148 during Wal-Mart’s Black Friday deals.

Wal-Mart will release all of its Thanksgiving to Black Friday offerings Tuesday.

Akshay Rao, a marketing professor at the University of Minnesota’s Carlson School of Management, said it’s a mixed bag of risk and return for retailers trying to woo Thanksgiving Day shoppers.

“If you want to open earlier or stay open later, you have higher labor costs and higher utilities costs,” he said. “The trick for retailers is to balance costs with the benefit — which is the profit margin of staying open.”

Macy’s, Kohl’s, Sears and Herberger’s have all announced that, like Target, they plan to open at 8 p.m. on Thanksgiving. Like Wal-Mart, Richfield-based Best Buy is opening at 6 p.m.

Target said Monday that its stores will remain open throughout the night and close at 11 p.m. on the day after Thanksgiving.

Target also will offer hundreds of deals online on Thanksgiving morning that will include almost all deals that will be available in stores. In addition, Target said it will feature 15 online-only daily discounts for two weeks beginning on the Sunday before Thanksgiving.

The stakes are high for retailers since the holiday season accounts for up to 40 percent of their annual revenue. The National Retail Federation, the nation’s largest retail trade group, expects an increase of 3.9 percent to $602.1 billion in holiday sales for the November-December period, up from 3.5 percent last year.

There’s also more pressure on retailers this year because the period between Thanksgiving and Christmas is six days shorter than in 2012.

Last year, even with earlier openings, sales didn’t fill up retailers’ coffers. Weekend foot traffic increased 3.5 percent according to ShopperTrak, but retail sales fell 1.8 percent to $11.2 billion.

Retail analyst Marshal Cohen expects more of the same this year. The frantic Thanksgiving-to-Monday period will front load the holiday spending but dilute the rest of the holiday period.

“Consumers don’t have more relatives or more money in their pocket,” Cohen said. “So once the dust settles, we won’t see too much growth overall.”