Taylor Swift Performs Calvin Harris, Rihanna's 'This Is What You Came For'

Taylor Swift fans got quite the treat Friday in Liverpool ... when she played an acoustic version of Ex Calvin Harris and Rihanna's hit, "This Is What You Came For."

It was her first "Eras" tour surprise song of the night, and Tay teased it saying, “Every single time I have an acoustic set, I’m always trying to think of things you might want to hear — maybe things that might be a little bit unexpected. Let's see how we did tonight."

Swifties went crazy for the tune, which was performed as a mashup with her hit "Evermore" album song "Gold Rush."

As fans know, TS wrote “This Is What You Came For” with then-boyfriend Harris.

TMZ broke the story ... Taylor wrote the tune, but used the pseudonym Nils Sjöberg.

She and Harris agreed it was a bad idea to let the world know they collabed as a couple because it would overshadow the song.

Swift previously performed the hit in October 2016 at the Formula 1 Grand Prix, and again at a performance in 2017.