Taylor Swift Overflow Fans Listen to Eras Tour Outside Mexico City Venue

Taylor Swift's international popularity was pretty obvious Saturday night in Mexico ... not only did she fill the venue, there were hundreds of fans who sat outside on bleachers ... just to get an earful.

Taylor performed in Mexico City Saturday night -- she's had 4 shows in the country -- and it seems there wasn't a venue big enough to satisfy all the Swifties.

The next best thing to seeing Taylor is hearing her, and that they did. Hundreds of fans plopped down to hear the Eras concert. The bleachers were actually filled to capacity and people were turned away.

During the show, Taylor began the show with "Hola!" ... and encouraged her dancers to speak Spanish during the show.

She told the crowd ... "Welcome to the acoustic section! Can I say that, to everyone in the back, you are absolutely incredible. I've been watching you all night. You've been so into it."

Her surprise song last night -- "Cornelia Street."  That was a big deal, and Taylor knew it, telling the crowd, “You guys have been beyond patient and supportive, and it’s taken us this long to come here and play for you, So I wanted to give you a song tonight that a lot of fans have been requesting the whole tour.”