MEXICO CITY — One of Pato O’Ward’s sponsors announced an appearance for the IndyCar driver just 20 hours before the event at a Mexico City mall.

They told him to expect about 120 people. But when fans began lining up 12 hours early, it was clear they underestimated.

More than 3,000 screaming fans packed all three levels of the mall, with 1,000 or so more stuck outside. When the Arrow McLaren driver arrived at the mall, getting dropped off more than a mile from the entrance, the fans outside formed a tunnel that O’Ward had to run through, high-fiving as many as he could.

“Man, they really made me feel like a pop star,” O’Ward said.

The fans carried posters that declared themselves “Patties” — like Taylor Swift fans are known as “Swifties” — and giant floating heads and were decked out in merchandise he sells from his own online store.

Among the most noticeable gear were the hats and shirts that said “Pato Who?” that were designed after IndyCar CEO Mark Miles said the reason why the series does not race in Mexico City was because event promoters told him several years ago that O’Ward was not as big a draw as Adrian Fernandez, a Mexican driver who competed for the series when it raced at Autodromo Hermanos Rodríguez.

O’Ward was so insulted that he leased a billboard near Indianapolis Motor Speedway that says “Pato Who?” and a second one is in the works. The brouhaha began when NASCAR in August announced that it would race in Mexico City in 2025 and O’Ward was incensed that IndyCar had been beaten to an event in his home country.

And those promoters who once told IndyCar that O’Ward wasn’t a big enough star to carry the series into Mexico? They saw firsthand during the Formula 1 weekend that O’Ward might be second in Mexican popularity to Red Bull driver Sergio Perez, but his charisma and fan engagement is so spectacular that he potentially can grow into the country’s most revered race car driver.