Beef patties aren’t the only thing sizzling at Burger King — and its booming business is taking a bite out of McDonald’s.

The fast food chain owned by Restaurant Brands International reported an eye-popping 5.8% increase in comparable sales at its US eateries – its highest growth in nine quarters – signaling that the Golden Arches face a growing competitive thread.

Chatter over the burger battle heated up in February when McDonald’s CEO Chris Kempczinski appeared to struggle to take a bite of the chain’s new Big Arch burger in a promotional video that went viral. Kempczinski took too long to bite into the sandwich — which he called a “product” — and then showed off a bite that many mocked as suspiciously small.

Burger King’s president Tom Curtis seized the moment to promote an updated Whopper – its first revamp in 10 years – including creamier mayo and a box for the multi-layered burger, posting a TikTok video of himself taking a huge bite.

The Miami-based company is also renovating its eateries to present a “clean image.”

Burger King honchos said on an earnings call on Wednesday that all of these changes are making an impact.

“One of the things we saw recently that gave us confidence,” said CEO Joshua Kobza, “is that during our Sponge Bob promotion in the fourth quarter we saw the the highest [customer] repeat rate for any of those promotions in a long time.”

RBI’s turnaround plan was launched several years ago when former Domino’s Pizza Chief Executive Patrick Doyle was appointed executive chairman, said restaurant analyst Mark Kalinowski.

“Burger King is cleaner and its operations have improved so you are more likely today to get a Whopper hot, fresh and to get it exactly how you ordered it,” Kalinowski said, adding. “So far the remodel has been a winner for Burger King.”

The redesigned stores are 60% smaller and feature natural wood, open ceilings, triple drive-thrus, external food lockers for pickup, and walk-up windows.

Burger King recently began touting the changes.

“You can’t wait for perfect, but we are confident that our guest experience will continue to improve,” Kobza said of the company’s eatery redesign.

McDonald’s, the largest restaurant company in the world, is reporting its latest financial results on Thursday and it’s unlikely to reach Burger King’s stunning 5.8% growth, Kalinowski predicted. 

RBI also owns Tim Hortons, Firehouse Subs and fried chicken chain, Popeyes, which saw a 6.5% decline in comparable sales for the quarter ended March 31. Comparable sales at Tim Hortons, which accounts for 41% of the company’s operating profit, was up 1.6%. 

The fast food company’s shares were down about 5% by late morning

RBI flagged “weak consumer” spending in Canada where Tim Hortons is the dominant coffee chain.