Heri Salazar was surprised Monday afternoon when he learned that his family’s south-side Mexican restaurant was in the hunt for Caliente’s Burrito Madness finale.

St. Mary’s Tortilla Factory, 1030 W. St. Mary’s Road, handily beat Paco’s Mexican Restaurant, 5563 E. Grant Road, in Round 3 balloting last week to advance to the semifinals.

Voting begins Thursday, Aug. 27, at tucson.com/mobilemadness

St. Mary’s Tortilla Factory faces a formidable challenger: Zivaz Mexican Bistro, 4590 E. Broadway, which beat challenger Taqueria Juanitos, 7089 W. Grant Road, by a nearly two-to-one margin.

Zivaz has experience mounting a successful Madness social-media campaign — the restaurant won Caliente’s Burger Madness in late 2013 and has been campaigning with nightly burrito specials and an aggressive Facebook presence since Burrito Madness started a month ago.

St. Mary’s doesn’t do Facebook.

Or Twitter.

The Salazar family doesn’t even have a website for the restaurant it has operated for 40 years.

“It’s all the customers,” said Salazar, who manages the restaurant.

If anyone is driving St. Mary’s Madness success it’s the customers, he said. They are loyal to a fault and passionate about the restaurant’s house favorite chile con carne — cubes of beef slow simmered in a rich red chile sauce — then wrapped in St. Mary’s in-house hand-tossed tortillas.

Salazar thinks those tortillas might be their secret weapon against Zivaz. St. Mary’s, he said, is one of only a few Tucson restaurants making tortillas by hand.

As for this weekend’s voting, Salazar said he’s not too worried.

“We’ve gotten this far with just doing what we usually do and it’s working out,” he said, adding that he has no plans to launch any last-minute push to get customers to vote. “We just let the cards fall where they may.”

Round 4 also sees the northwest side neighborhood favorite Olé Mexican Grill, 2080 W. Orange Grove Road, taking on El Güero Canelo, which has several locations including 5802 E. 22nd St.

Olé bumped off Tania’s, 624 N. Grande Ave., by more than 60 votes. El Güero toppled Nico’s, a local chain with multiple locations, by 14 votes.

El Güero is on Facebook, but it has not promoted Burrito Madness. Instead, El Güero is using its social media to let customers know about its west Phoenix restaurant, set to open in a week or so, said office manager Ciria Juvera.

Juvera said she believes El Guero is still in the Madness hunt because “we make really good burritos” and fans of those burritos are leading the charge to vote.

“We have loyal customers,” she said. “Most of it is word of mouth.”

Contact reporter Cathalena E. Burch at cburch@tucson.com or 573-4642. On Twitter @Starburch.