Popeyes has overtaken KFC as the No. 2 chicken chain in the U.S., a decade after Chick-fil-A first unseated KFC from the top spot.

Chicken chains' battle for stomachs — and dollars — has become more aggressive in recent years. Chick-fil-A moved from a regional player to a nationwide chain that trails only and in annual sales. 's Popeyes launched a in 2019 that turned into a blockbuster menu item and ushered in the chicken sandwich wars. Burger chains such as McDonald's and jumped onto the trend and added their own offerings, leading to poultry shortages.

In the fray, ' KFC has lost ground. In the past year, its U.S. market share fell to 11.3% from 16.1%, according to Barclays research.

Similar to KFC, Popeyes lost market share in the past year, but still retained enough to leapfrog its rival. The chain saw its U.S. market share shrink to 11.9% from 15%, according to Barclays.

Blame Chick-fil-A, which saw its market share expand to 45.5% from 38.3%. The privately held Atlanta-based chain is more dominant than ever. Chick-fil-A is still closed on Sundays, but industry experts credit its customer service, short menu and efficient drive-thru lanes for its success.

KFC's domestic business has struggled to keep up with the competition. It took for KFC to respond to Popeyes' chicken sandwich. The chain also lost longtime U.S. leader Kevin Hochman last year to Brinker International, where he now serves as CEO.

KFC did not respond to CNBC's request for comment.

Popeyes, on the other hand, has used the popularity of its chicken sandwich to introduce customers to other menu items and to fuel new restaurant openings. More recently, the chain's Sweet 'N Spicy Wings became its most popular launch since the chicken sandwich.

"Game on, Chick-fil-A," Restaurant Brands International Chair Patrick Doyle said in mid-September at Scotiabank's Back to School Conference, responding to a question about the chain's new spot as the No. 2 chicken chain.

Popeyes President Sami Siddiqui said in a statement to CNBC that the chain is still in the early innings as it tries to become the most loved and visited U.S. chicken chain.

"We view this special milestone as an indicator that we're headed in the right direction with much more growth to come," he said.